Some time ago, I bought a copy of the Pathfinder Beginner Box (reviewed here, here, and here). I still think about running it as a complete (E5-style) low power game, perhaps with a d20 supplement such as The Lost City of Barakus (that might be a fun G+ campaign). The one thing that I have decided that I absolutely must change is how at-will magical powers work. The same is true of the recent D&D Next playtest materials. The chassis is something I would enjoy playing, but I really dislike limitless powers, from both style and gameplay standpoints.
First, I would just remove cantrips that solve resource problems (such as light). Second, all other cantrips would require a short rest to prepare. Five minutes each, so two cantrips could be prepared per turn (important for things like torch duration and wandering monster checks). Diegetically, cantrips would be exactly the same thing as other vancian spells; they would just require less work to prepare. In game terms, they would function like Fourth Edition encounter powers. Thus, your PFBB wizard would get one free force missile (or whatever it’s called; I can’t be bothered to look it up right now) per combat.
I readily admit that this is not meaning first design, but it is “meaning based” design. And yes, this decreases the power of the magic-using classes. I don’t see that as a bad thing. In essence, there would be two kinds of vancian spells: the kind that require deep concentration and a fresh mind to prepare, and the minor cantrips that can be prepared given a few minutes.