While it isn't my thing from the few gearheads I have known most speak highly of them as a entry point into learning the ins and outs of how to work on small engines. Parts and the like are pretty cheap and highly available as far as Motorsports prices, and most of it is less replacing things and more tuning and timing things. Whatever the hell that means, lol.
I think they probably are on the same level as working on lawnmowers and chainsaw engines, only more for fun then doing lame chores.
Seriously nothing killed the cool factor of chainsaws for me then having to actually use them for their intended purpose.
Anyway back on the topic of bikes, if you already have a interest in it and got a bike already then I say go for it.
Just don't spend too much on your first project. Get one of the better reviewed low cost kits to dip your toe and see if you like the hobby. Then if you find you do then go nuts with your next build.