3.5 Why no scaling on sleep?

[Starbuck_II]

Sleep is an encounter-ending spell on low levels that has a unique balancing factor to make it all but useless later on. That's not a good thing, but then there's no real consistency on how useful low-level spells should be as you go up in levels. And at the end of the day I don't think a 1st level spell that can take several opponents out of the fight is a good idea anyway.

Color Spray still works unlike sleep at higher levels (no HD Limit, just less effects).
Extended Color spray is a very strong 2nd level spell (few 2nd level can match, Pyrotechnics if near flame comptes well though).

[Jay R]

The problem I am trying to fix is emulating a brass dragons sleep gas on a Bard with existing mechanics without unbalancing everything.

If you're trying to do it with existing mechanics, then don't use the sleep spell. The existing mechanics for that spell don't work like that.

[Kelb_Panthera]

It was my understanding this scales like hold, charm, and dominate; by taking higher level bits of the chain.

Sleep
Deep slumber
Symbol of sleep (in a box, obviously).