To repair, rebuild, or toss?

Depending on what the $600 gets you.  V-Caps, Audio Note non-magnetic resistors?  If those parts are going in then upgrade the unit.  But if it is only installing basic parts brands then no.  We upgrade audio components old and new every day with fantastic results.  Usually much better than what you can purchase as new gear.  Most gear does not have the parts I mentioned inside.  Those who recommend trashing the Rotel have never had anything upgraded with these parts so they have no idea what the sound improvement is.

Happy Listening

If you really loved the Rotel and it checked off on all the boxes you needed, then maybe a rebuild would be in order. It sounds like you are looking for an upgrade so I am not sure that is the case.  Suggest you move on.

As far as upgrading parts with premium caps, etc. not sure I would do that to 20 year old circuit boards/associated aged components.  Could be a big investment with limited duration return.  If it were a newer amp, component upgrades would make more sense to me.

I used to own one of the predecessors to that amp, a Rotel RB 980BX. Bought it used for $300 many years ago, Great amp for the money. That being said, I would never spend hundreds to rebuild it if it had died on me. 

You have received some great suggestions from other members. I don't think you need to spend $10,000 for a great amp. Unless your enamored with your preamp, I I would also check out some modern integrated amps. Amps from makers such as Hegel, Rega, Primere, Arcam all make integrated amps with over 100 WPC for under $5K. Just a thought.

I wouldn't repair or refurbish it...it was a good budget amp in it's day (I had one) but current amps from Schiit or Odyssey I think are significantly better, and can be found for $600 used but only a year or two old, and new for not much more...those are brands I've owned but there are many others in your price range...

Unfortunately, compromises in tonal balance and subtlety are sometimes encumbered as well, and the resulting tonal inaccuracies are often flaunted as a distinctive "character."   ~ Stereophile

Not worth it.