This weekend I installed Vista Home Premium and then rightaway FSX.
I started FSX without any cfg fixes because I wanted to see how it runs on clean config. And I was surprised to see how smoth it was. I don't know if it's just my imagination, but to me is noticable smoother and a bit faster then before on XP with fixes. Most of the time I have 30fps (20 in city) and no hickups.
It also look nicer somehow - but I'm sure that this IS my imagination
Perhaps Vista and FSX-SP1 and even DirectX10 SP, will indeed make this game more playable.