Even though I'm ready to spend a little extra for better libraries I don't have an unlimited budget, so I guess what might make more sense now would be to buy some good libraries in the mid price range and look at a bigger investment later on.
One library I won't recommend is VSL. It's been around along time now and so there are plenty of some staggeringly good demos, but when you look into how complicated and time consuming it can be to get that kind of result, all the fiddling knocks the creativity out of you.
I bought the original Symphonic cube for EXS, and the performance tool didn't quite work and the oboes and brass were really weak. So then I upgraded to the Vienna instruments, thinking it would all be that much better. (like I'd spent £3000 on something that didn't quite work, it would be good to pay just a mere £2000 to get it really functional).
NB: one issue I had was that that many stereo samples were badly out of phase (ie NOT mono compatible). When I contacted support about this, the reply was that most pros would use a stereo image plugin to reduce the width anyway. No attempt to address the issue beyond making you fork out for the upgrade.
Having done that I'm still disappointed. There seems to be a tacit understanding that the original library had rom for improvement, but instead of letting old loyal customers have an upgrade, you just have to keep buying and buying, as if it's a crock of gold at the end of a rainbow, but turns out just to be a crock.
</VSL rant>
The other library I have is EW Symphonic Gold, and as has been pointed out, that is recorded with more ambience, so works really really, provided that ambience fits in with your track.
I found its easier than Vienna for getting something very impressive sounding, though does have some restrictions due to the ambience being part of it.
Beyond that, I still have great respect for the cheap and extremely cheerful Garritan.
I echoe all the stuff about fast and many drives, processors, RAM to the max. And its only going to get worse as libraries get bigger.