Rikki, very early on in my conversion to the software approach I used top of the line sampled acoustic instruments. Over time I backed away from that and used these kind of instruments only for my favorite instruments. I would use smaller sampled instruments for such things as electric guitars, electric pianos, etc. This was more from a cost consideration that I took this latter approach. From a computer capability perspective I could keep on using the higher end sampled lead instruments. You need to balance this however when using a software system for live performances. Smaller sampled instruments tend to load somewhat faster and you can load more of them.
As you know, it is not just the size of the sampled instrument that determines its quality but a whole lot of other things as well (mics used, venue, and so on). I tend to buy these instruments from reputable developers, e.g., Garritan, VSL, Bardstown, VRSound, East-West, etc.
[This message has been edited by Frank L. Rosenthal (edited 09-22-2007).]