It's a tough question because it's a weird situation. I've had an Index for about a month. VR is simultaneously radically superior to, and significantly worse than, TracIR. If you just want to go out and fly around feeling as if you are in a real airplane, VR is fantastic. It's so similar to actual flying that I think you could do legit flight training with it. Administrative stuff like tanking, and pattern work (especially recovering on the Tarawa) are so much better that it's almost a different activity. But... If you want to fight; not so great. You better already know your cockpit because its hard to read anything. Even medium distance targets are blurry. Frame rates go way down and you'll have to make real compromises on eye candy.
I was going to return my Index. I felt like it was super cool but not quite there (this is true btw). RMA in hand I put my wife in VR in the back of a Tomcat. We did a short exposure flight; Launch, hit the tanker, watch the wings as you go supersonic, trap back on the Stennis. Her verdict was keep it. VR can be an almost disturbingly real experience but there are currently lots of compromises that have to be accepted to get there.
PS - obviously I kept it ;)