From my own experience with going to a technical/vocational college, the best way to "further" your experience and education is find a shop and become an apprentice. If you can't find one that accepts apprentices, get a job there and become friends with the mechanics.
Another option is self education. Buy a junker or two, work on them yourself and study/research as much as you can. This takes more drive, but personally, I find it more rewarding.
As for MMI, I don't have any experience with them. I've looked into the motorcycle mechanics program as well, but have read very, VERY mixed reviews. Something to keep in mind, their goal is to give you BASIC knowledge for ENTRY LEVEL positions. In other words, you'll have minimal education for a job you could probably get without going. This isn't to deter you from going, just my own research and experience with these types of schools.