What if broad-spectrum Polymorph had to be prepared with a specific form in mind?

[Segev]

Polymorph and its ilk are on the list of things that tend to make casters 1st-tier characters. One of the problems with the later specific-form spells tends to be that it balances okay for Wizards and other prepped casters, but hits spontaneous casters rather hard.

What if, instead of having myriad written-up specific-form spells, we kept the original Polymorph et al...but prepared casters have to learn them form by form? Spontaneous casters retain the spontaneous ability to polymorph (or Alter Self, or what-have-you) into anything the spell allows when they cast it, but prepared casters have to purchase each individual form as a new and unique spell. Likewise, they must prepare them each as separate and unique spells.

Ignoring the other things that make casters tier-1, how would this shift the relative balance of these spells?

[Fouredged Sword]

They would be weaker, but not by much. Really, there are a few forms that are good to use, and in practice, players deviate rarely, and only to do specific things.

[DR27]

Don't allow polymorph. Just don't. Dispacer form, troll form, dragon shape, etc all fill the role without being omgIwin!

[shylocke]

My DM runs all polymorph spells as when you get the spell. You choose a number of forms that you know(can't remember his equation for it). The number of forms went up as you lvld up though. He did the same for summons. You got to forge a link with a specific extra planar creature.

[Drachasor]

Personally, rather than limit it to one form chosen when you prepare it, I'd rather see the combat ability taken away, duration extended, and have it provide good non-combat forms (like mice, cats, and so forth).