I've thought about LT and VO2 testing. I'm not sure how I could use the information for anything other than a scientific curiousity, though, so I've never considered it much further. Field testing seems much more applicable to training and racing.
I find the same thing with cars I work on. New engineers want to do all sorts of science experiments, which, no doubt, are cool in a geeky sort of a way. When I ask the question, "Now you're going to spend $XXXX to do 'Y'. How is that going to make the car faster?" I often get blank stares. If you have everything in place to actually use the information (i.e. simulations, etc.), then you can use the info. If you can't afford the whole ball of wax, though, you're really just pissing in the wind.
It's the same deal with lab testing in cycling. If you can do regular tests, adjust your diet (medical 'preparations' in times past) and training schemes and possibly even the races you do (i.e. you're a pro), then it makes sense. If you're not into it that serious, though, it's more of just a data point in space, which tells you quite little on it's own. You'd probably be better off spending that money somewhere else.