I've basically had some form of altitude sickness every time I've flown in to Colorado and tried to do something athletic the following day. I've puked all over the Maroon Bells trail in Aspen and wound up in the ER there, so by comparison, the A-basin experience was much better. :/ I remember either @jimmy or @James saying that they knew I was doing better when I said I wanted to go shopping (which meant I was probably still not thinking clearly since I actually don't like to shop)!
For me, it takes my body too long to adjust to being at that high elevation that if all I have is a short weekend, I'm better off going to Utah.
You're the perfect candidate for skiing Hokkaido...