Absolutely agree. I'm a huge proponent of yoga, as an important piece of anyone's fitness routine. The core and balance work is great for MTB, and the flexibility work (esp. hip opening) is very helpful for cyclists. But the piece often overlooked, and I think perhaps most important is how a regular yoga practice (esp. with a well trained instructor guiding/correcting your poses) is the increased mind/body awareness. I think this is a big part of my improvement on the trails. Just the sense of where my body is relative to the bike, and an increasingly unconscious ability to make minor adjustments. Believe me, I know I still have tons to learn, and plenty of room to improve - but at same time have made giant jumps in what I can do - and in my confidence in trying Heck, I even was going over little dirt jumps over the weekend. Not getting very airborn, but trying.
The winter before last in addition to my normal yoga practice, I took a couple of series of classes that were either bike/yoga or bike/strength training. Indoors on compu-trainers with a local tri-athlon instructor. First 45 minutes was on trainer, last 45 minutes either yoga or a circuit training session - both designed towards a cyclist. Hope to do same this winter.
(and do you like reformer work? Never have tried that...have done mat classes)