Yay!! Well done!!
I don't know how it works where you are but I just cat'd myself up to Masters B 35+. I never win anymore but I love racing in that group.
Yes, mtn biking seriously improves your cyclocross skills. The only chance I have of being on the podium is in the more technical races, then I have the advantage of my time on the mtn bike to help me. In the cardio hammerfests, I am sunk.
I got beat this weekend by a friend who for years I've known has the potential to beat me but she just didn't have the bike handling skills... well, on a not so technical course, she can beat me now. I've still got her on the more technical stuff. Maybe to need to actually train a bit.
Congratulations again! Keep having fun. That's what it's all about.
ETA: I *always* race in knee highs, no matter how hot it is. Just another reason to love cross.
Living life like there's no tomorrow.
http://gorgebikefitter.com/
2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS