I think if you keep your cost down (no rebuys, add on only if in real good shape) then they can be worth it. As far as the time involved (getting bored) try opening some fake money tables. I found them to be a great place to drop some chips. You can have a little fun being loose on them, while protecting your stack in the real money
I also like to open CC 1/2 screen sometimes late in a tournament when I get bored. Browse some of the MTT strategy posts. Occupies your time while reminding you not to donk out late.