Well, I honestly don't see a big difference between multiclassing between base classes and prestige classes.
Sometimes, Prestige Classes are very similar to a base class and could be seen as an "extension" of that class, rather than actual multiclassing, but often, this is not the case, and there really is no difference between multiclassing into another base class or the prestige class then.
However, the requirements are rarely a real hindrance (only for exceptionally weak PrC), as they often include skills and feats, which you pick anyways, and simply set a minimum level at which your character can start evolving into that class. Only, if you want to qualify for multiple prestige classes, but that's nothing I find should be made easy, really. Prestige classes are still something special and shouldn't be racked up just to tap the power of several of them.
Prestige classes are generally better, but also have requirements to balance this. But what balances a character without prestige classes against a character with prestige classes (i.e. a straight wizard versus a wizard/<arcane prestige class>). The requirements? Hardly. That's where the multiclass penalty (house rule!) comes into play. Works for us, doesn't have to for you.
Bye
Thanee