One nice thing about E6 is it limits your design canvas. Four spell levels is limited enough that you can actually think about how things should work.

Novice spellcasters can cast 0 level spells all day, or 1st level spells a few times a day. Veteran spellcasters can cast 2nd level spells, Master wizards and such can cast 3rd level spells.

Looking at Haste as a model, we have 2 derivatives. Snakes' Swiftness (Druid 1, Sor/Wiz 2) and Mass Snakes Swiftness (Druid 2, Sor/Wiz 3).

1. Snake' Swiftness. Single-target, one-round haste
2. Mass Snakes' Swiftness. Mutliple-target, one-round haste
3. Haste. Multiple-target, multiple-round haste.
Honorable mention, Haste 5E version: 3. Single target, multiple-round haste

From the other end of the scale, Bless is perfectly adequate, but bland.
1. Bless. +1 to hit. (5E version, +d4 to hit, 3 targets)
2. Elation, +2 to STR, DEX, +5 to speed.
3. Prayer. +1 to hit, damage, saves, enemies take -1 to hit, damage, saves.

I like the way 5E handles Bless. Rolling a die is easier for people to remember than adding a number, and often other players remind forgetful players to roll the d4.

The improvement curve is much less steep for the Bless chain than the Haste chain. There's a reason that Haste is a staple and Prayer is not. Extra attacks are more fun than favorable math.

So, looking at the lessons of 5E (rolling extra dice > adding numbers), what are some alternatives for the Bless chain?