I think the DR upgrade is around 2K so it would make better sense to buy a previously owned DR and sell the plain SC if there is a market for it. The last one I saw went around 1300 pounds, average seems to be around 1500 pounds.
Never heard a 252 with non-DR SC but by most accounts the SC DR was a big improvement for the 252.
But no use in switching out the 252 for a new one, just get it serviced one of these years, being 10 years old it is in the recommended service interval. Naim will add the latest updates, if there are any, as part of the service.
As for the SC, as bruss (not Dunc!) wrote it usually makes more sense to sell the non-DR and buy a used DR, in most cases. But as the DR upgrade is around 2K as bruss (not Dunc) wrote, do the math depending on used SC DRs that you find and the prices for non-DR that you can expect when selling
That makes sense. I am in a similar position. Find a SC DR for my 252 and move the current SC on to the study with the 82 or sell the SC and buy a second olive hicap and some new music and a bottle or two of something pleasant to enjoy it all.
I think the decision re: keep current supercap for superine and get a lightly used supercap DR for 252 is a good one. Your current supercap can be serviced relatively cheaply, especially if using Class A. Out of the two boxes, it’s more likely the supercap that’s gone ‘off’. The 252 may be ok for a while yet.
As far as the 252 is concerned, if you have a good clean example with a well balanced volume pot, I would definitely keep hold of it and just get that serviced when the time comes. That too can be relatively inexpensive and it will come back performing like a new one for far less £££’s.
From what I’ve read, I think you will get a nice improvement from the DR power supply on the 252.