Reel to reel repair - is it worth it?

You have to ask several questions.
How good was the unit originally? Was it at the Tandberg or Revox level? Does the fixit guy have any experience with R2R? Some, like my Tandberg are mechanical monsters. Three motor designs can be somewhat less complex, but than you can toss in auto-reverse and there 'ya go.

I'd find a pro for the fix.

Over the years I've had a BUNCH of 'em....Sony TC series in both 3 head and 2 head. Tandberg 3000x. Teac 4010S (nice big meters) and an Akai with cross field heads.

Even if the machine is perfect, you'll find the tapes to be a limit. I have no idea if you can get recording tape today or what is available. I used to buy Scotch 207? 203? by the case. Head wear, demagnetizing and more can turn into hassles. Clean the heads? yep.

If you get it working, I'll send you...for shipping....a DBX compressor / expander you can play with. Should buy you a few db on the snr.....drat that tape hiss.

At last springs THE Show in Newport Beach I saw several R2R based systems whic h sounded terrific.
One of the system owners had access to 'master tape' level recordings. Too bad each pass thru the machine takes a little off the top.

So, such systems are still out there and sounding good. Only you can decide if upkeep and material sourcing issues outweigh the 'cool factor' and sound.