McCormack REV B upgrades. Better than a new amp?

Unfortunately the caps by far are not the biggest problem.  McAmps of that age have input boards that are now failing, which is fatal because there’s no repair for it so the amp is basically toast and requires a total rebuild.  You can speak with Steve McCormack about it at SMcAudio (I did) where they still do their awesome mods for the DNA amps and their other stuff, but I wouldn’t touch that amp if I was you.  Caveat emptor. 

I think in the used market you're better off waiting for a Rev A unit or better. Given the cost of these units on the used market vs. buying one (new or used) and upgrading it makes buying an already upgraded amp a great bargain. I'd skip Rev B and get either a Rev A or Platinum given the discount on the used market and the significant upgrade in performance. Best of luck.

Oh, forgot to answer your question about reliability. I'm the third owner of my 0.5 Rev. A and have had it for 14 years with fairly heavy use. The only thing I've had to do is replace a fuse, and as far as I can tell the amp sounds the same as it did the day I got it. Steve's also great about support if ever needed.

You should consider contacting Steve McCormack. I've found him to be most helpful, and I'm sure he or Chris would be upfront with you on the differences you can expect between the Rev. B and Rev. A, etc. When I spoke to Steve a looooong time ago he implied there is a big difference between B and A, but can't remember specifics (I think the power supply was significant) and what the final effect on sound was.

I seem to see 0.5 Rev. As come up from time to time, so the wait might not be as bad as you think if it's truly a big stepup on performance. I'll certainly keep my fingers crossed for ya.