My wife won't let me touch her bike either.
The cars I can take them apart and fix them.
But not her bike, the thing is running so lean its killing me, but no I can't take it apart.
For advice on how to do it, I think the women of BA.com will be your best guide.
I have always hated the "used car salesman" approach of be a man ****** her off.
Screw that. I would want her to go out and spend 10 thousand without telling me.

On a side note I did get her good one night a few years ago. I had headed out all day to drive around. I ended up test driving a couple new trucks. This was when the "24 hr" test drive had just started, so I took it home. Got home, causally dropped the keys on the table and waited for her to look outside. It was awesome, I let her rant and scream for a good 10 minutes before I couldn't stop laughing. Still didn't get that truck though.