A 588

Practiced Spellcaster can apply to a prestige class, but it will only affect spells from that prestige class, not from other classes. (This is useful for prestige classes such as Assassin or Blackguard.) Only your Eldritch Theurge spells would gain the caster level boost. Since all you have are Wizard spells and Warlock invocations, this is quite useless.

Practiced Spellcaster does also increase the caster level for non-spell abilities, but since Fiendish Resilience and Damage Reduction don't scale with caster level and your caster level for supernatural abilities is already equal to your HD unless otherwise stated, this is also useless.

Incidentally, I believe there is some debate as to whether spellcasting-advancing prestige classes count as spellcasting classes in the first place. (Eldritch Theurge has a class feature called "Spellcasting" that gives you spells, so I am inclined to say it is probably a spellcasting class, but I can't find any rules to support or refute this conclusion.)