I would say the only relevent use for Flight sims( FS98, FS2000 ) in relation to what you guys do in the pointy end would be as a type of famil/proceedural aid. e.g. this does that, see how those needles move in relation to each other.
As an avionics engineer I find that the main problem is that how crew use intsruments in flight does not necessarily relate to the way we test them on the ground. I play around with FS98 and that, along with jumpseat trips, has given a better understanding of how an aircraft is operated by crew as opposed to what I know of how it works. If I understand what the crew are talking about with a defect I can trouble shoot it much better.
I don't think it would help in piloting an aircraft. I can fly the 767 on the computer but I can't fly for !!!!! in a real aircraft.