While agree with you regarding the mask being a gimmick, I wanted to correct something minor in the next statement, having had experience training for high-altitude and living at just over 5,200 feet right now.
The first and second day will not affect you that much after arriving at the higher elevation. While good physical condition is IMPERATIVE, the third day will make you wonder where all your fitness went. That is when you body starts to transition itself to the lack of oxygen percentage. After that, you will be better and better after that day. Something to think about when planning your trip.
Then, of course, living at high altitude would be the best thing. When I was bicycle racing against other people, my high altitude training was REALLY beneficial. I could recover quicker, pedal faster, keep my base level higher, an so on and so forth. The downside to this was heavier thicker blood, which for older people could be a concern.