Possible Use of Residual Magic & Spell Rehearsal Feats?

[Droningbass]

I've been looking for some advantageous feats for an Ultimate Magus build, and I stumbled upon two that I think would work splendidly together (if I am reading them correctly). Here are the two feats at which I'm looking:

Residual Magic - Complete Mage p. 46

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Residual Magic [Tactical]
You can use the lingering energy from a spell you cast to boost the effect of a later spell.
Prerequisites:
Spellcraft 12 ranks, any metamagic feat
Benefit:
The Residual Magic feat allows the use of two tactical maneuvers. Enduring Potency: If you cast a spell from your daily allotment of spells, then cast the same spell from a scroll or wand in the next round, you can treat the second casting as if it had come from your daily allotment of spells for the purpose of caster level, save DC, and any other effect of the spell. For example, if Hennet the 10th-level sorcerer casts magic missile, then activates a wand of magic missile (caster level 5th) in the next round, he can treat the wand's magic missile as if he had cast it (giving him a greater range, number of missiles, and so forth). Lingering Metamagic: If you cast a spell affected by one or more metamagic feats, and then cast the same spell in the next round, you can apply any one of the metamagic effects from the first casting to the second casting, but without any change to the spell's level. The second spell doesn't count as being affected by a metamagic feat for the purpose of this benefit (that is, it doesn't entitle you to apply the metamagic feat to a spell you might cast in the following round). Only spells you cast using your own metamagic feats (as opposed to metamagic effects from magic items) allow this option to function. For example, if Hennet uses a 5th-level slot to cast an empowered lightning bolt, in the next round he can use a 3rdlevel slot to cast another empowered lightning bolt. If the first spell was a silent empowered lightning bolt, he could apply the effect of either Silent Spell or Empower Spell to the second casting of lightning bolt, but not both.

Spell Rehearsal - Races of the Dragon, p. 105

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Spell Rehearsal [Tactical]
Casting the same spell several times in a row or at the same target enables you to perfect it.
Prerequisite:
Caster level 1st
Benefit:
The Spell Rehearsal feat enables the use of three tactical maneuvers. You can only apply one maneuver at a time to a single spell.

Persistence: To use this maneuver, you must cast a specific spell two or more times in succession, and the spell must be one that allows affected creatures or objects a saving throw. You can take a move action after casting the spell once before casting it again, but you cannot take any other standard actions between successive castings. On the second and subsequent times you cast the spell, you add a cumulative +1 to the spell's save DC. If you cast any other spell after starting to use this feat or take any other standard action, the persistence chain breaks and you must begin anew.

Refined Targeting: To use this maneuver, you must cast a specific spell two or more times in succession, and the spell must be one that requires an attack roll to affect a target. You can take a move action after casting the spell once before casting it again, but you cannot take any other standard actions between successive castings. On the second and subsequent times you cast the spell at the same target, you gain a cumulative +2 enhancement bonus on the attack roll to deliver the spell. If you cast any spell that does not require an attack roll or take any other standard action, the refined targeting chain breaks and you must begin anew.

Persistent Targeting: To use this maneuver, you must cast a specific spell two or more times in succession, and the spell must be one that allows a target to apply spell resistance to the effect. You can take a move action after casting the spell once before casting it again, but you cannot take any other standard actions between successive castings. On the second and subsequent times you cast the spell at the same target, you gain a +2 bonus on caster level checks to overcome the target's spell resistance. If you cast any other spell or take any other standard action, the persistent targeting chain breaks and you must begin anew.

Special: This benefit applies to spells you know or have prepared as well as spells cast from items such as wands and scrolls.

So, if I'm reading the entries for these two tactical feats correctly, they allow for some significant benefits at the cost of very few spell slots. For example:
-In the first round of combat my Ultimate Magus casts an Empowered Fireball casting a prepared Fireball spell slot and sacrificing a spontaneous Level 2 spell slot using the Augmented Casting ability from the Ultimate Magus PrC.
-In the second round he casts another Fireball (either from his own prepared spells, or through the use of a Pearl of Power) which is automatically Empowered by the Lingering Metamagic maneuver from the Residual Magic feat, and also receives a +1 to its Save DC from the Persistence maneuver from the Spell Rehearsal feat.
-In the third round he casts a third Fireball, this time from a wand (or scroll). This casting is automatically Empowered and is treated as if it had come from his daily allotment of spells for the purpose caster level and Save DC by the Enduring Potency maneuver from the Residual Magic feat. This spell will also receive a +2 to its Save DC from the Persistence maneuver from the Spell Rehearsal feat.

So, to get three rounds of Empowered Fireballs with full damage dice/improved Save DCs, all you have to do is spend two Level 3 spell slots, one Level 2 spell slot, and one charge from a wand (or one scroll)! It sounds like an excellent trade-off for two feats, and it could be utilized with tons of other spells!
This could also be used to increase chances of beating Spell Resistance (using the Persistent Targeting maneuver of the Spell Rehearsal feat) instead of increasing the Save DC. The Spell Rehearsal feat can also make repeated uses of rays almost never miss (adding a stacking +2 to Attack for each repeated ray!).

I feel like these two feats have gotten absolutely no attention from what I've found in Wizard and Ultimate Magus builds online, and I feel like the Ultimate Magus takes a special advantage of these two feats in particular. Am I reading/interpreting these feats correctly? Does this look like something that would be feasible? Does this seem like something that would be worthwhile to a spellcaster?

[Zanos]

-In the third round he casts a third Fireball, this time from a wand (or scroll). This casting is automatically Empowered and is treated as if it had come from his daily allotment of spells for the purpose caster level and Save DC by the Enduring Potency maneuver from the Residual Magic feat. This spell will also receive a +2 to its Save DC from the Persistence maneuver from the Spell Rehearsal feat.

You can't use enduring potency to metamagic a spell if the previous spell was metamagic'd by enduring potency.

You are correct however that residual metamagic is a solid feat. Spell rehearsal is a bit more situational because it requires you to spam the same spell. Not bad if you were planning on doing that anyway, I suppose.