I also vote for "tough call to make over the internet".
If it's in good shape, it's often a lot easier & just as well to leave it. Make the holes you need, fish the wires, patch... It's definitely do-able, we do it all the time, here - we have a lot of plaster & lathe in NYC. In fact, that's how I learned what I know about electrical - used to do a lot of plaster-repair work for an electrician.
If I ripped out all the plaster & sheetrocked, in every ceiling or wall he needed to fish wires through? A whole lot of 2-3 day jobs would have been month-long jobs. It's a whole extra order of magnitude, really.
This all assumes you know how to patch P&L. Don't imagine you can use a remodel recessed fixture in plaster, the plaster's too thick for the clips to work.
Drywalling over the old plaster can work, and sometimes, it's the best solution. If you have localized damage - say, under a bathroom - but the rest of the ceiling is sound, and it's an occupied space where you don't want to have all that wreckage? The best thing is to remove just the damaged part, shim out the joists/studs to the same level as the sound plaster, and sheetrock over the whole lot with 5/8" drywall. (1/2" is too floppy, will telegraph irregularities too much, & look like crap)
It all depends on the condition of the plaster, really; and that's a judgment call that needs an experienced eye, on-site, can't be done over the 'net.