I did exactly this. I thought since I had a new road bike, i'd get rid of my MTB. Then I decided to learn more bike repair tuning it up. Now I am gonna go further and putting 3-400 into it with all new parts. I'll have a new MTB thats got way better parts on it than a new $400 bike. A back up bike is always nice to have. Don't have to take my nice hybrid on local errands either.