Thanks, Andion, but we knew that. That's what this thread is about: Is this limitation a good idea, or not?
IMO, it's not a good idea. Those spells that were exposed as broken via the meta-magic feats have been (mostly) fixed. In fact, even with multiple meta-magics, the feats themselves are still (mostly) lame.
Widen Spell is the worst of the lot, actually. Only a very few spells are worth this kind of trouble, and only against hordes of small mooks.
As for the doubly widened fireball => the area is doubled twice, not doubled sequentially. (Total area would be 60' r, not 80' r.) That's the way all doublings, triplings, etc work in 3e D&D.