Well well well... it seems that I've been a bit over-excited lately with Pathfinder RPG. It's a good idea to be D&D 3.5 compatible, but currently it's remaining too close to the original to become a game on its own.
Take a new D&D player for example, he'll have a hard time finding differences between both! And IMO that's not a good thing. To sum things up: PFRPG isn't enough "added value" compared to 3.5... Yes indeed, I am against full retro-compatibility with D&D 3.5.
I bet that if you take a random adventure, run it once with a group of non-hardcore players using 3.5, erase their memory, run it again in PathfinderRPG, there won't be any significant difference regarding the actions they chose to do and the effects those actions had on the environment (provided they chose the same character classes for both games). If so, what's the point in changing the game?
I'm reading some people saying very interesting things on other 3.5-evolved systems such as Monte Cook's Arcana Evolved. Maybe "the truth is out there"...
In any case, when looking at the "bigger picture", I don't find Pathfinder RPG necessary.