I spent 2 weeks in a Kenyan running camp in New Mexico. Came home fitter despite being laid off for some of that time with a massive blister, sick and spending way too much time in airports (wouldn't recommend united Airline for any internation flights). The impression I got was the higher the better and I'd do it once a year if i could afford it - just for aerobic fitness. Obviously there's a lot more to boxing than just aerobic fitness and I'm not sure how high this particular place you're talking about is but needs to be pretty high to be relevant I think.