Kermit said:
I find sleeping one night at altitude helps me tremendously.
I am lucky though, living in Tucson I have 8000' mountain in my back yard. I go there just about every weekend to hike or bike, to prep me for Colorado.
Those short romps up to 8,000ft don't actually aid in your acclimation, but they do help bolster your aerobic efficiency. Most likely, those trips up to 8,000ft reap positive gains with increasing your Vo2Max. If you're riding and hiking, it can also help improve your lactate threshold level a teeny bit. This is all part of the train high, sleep low method replicated by altitude tents.
True acclimation takes anywhere from 5 to 9 weeks and comes from sleeping at high elevations. Everyone is different. I do great on day one. Day two blows.
There's a product called EPnO that helps build good blood health. Paired with a highly aerobic preperation period prior to your trip, it can help with your aerobic efficiency enough to stave off some altitude woes.