Here is a meta-paper on the issue: paper link
I had always heard that the “fly-in fly-out” strategy was second best to proper long term acclimation (i.e. better than the intermediate strategy of showing up a day or two before), but apparently there is not really much data to back this up.
High elevation does make for a solid home-field advantage, but high elevation teams can’t train as hard as lower elevation teams, so there are some tradeoffs (especially for max speed / max-power sorts of efforts).