John, guess I will chime in here, while I currently own Croft Micro 25/Series 7 amps, I also have had experience with the Croft phono integrated. I also used a Naim Uniti as source into these Croft’s, and also own Naim Nait XS3, along with ND5XS2 streamer. While I haven’t done any comparison to Rega’s amps, I would imagine there will be others who have.
In my opinion, the Croft for starters will work pretty well with your Spendor I would think, and as I have found, the Uniti really is a very nice source, probably better than many would give credit. To me, I think the Croft/Naim work well with one another. I think the Naim helps give the Croft a bit of pace, but it is nothing pronounced.
The Croft integrated is a bit more laid back, or relaxed compared to the Naim XS, or Uniti used as all in one. I have owned Naim systems for many years, and really enjoy them. The excitement and drive is to my ears, somewhat addictive, and I manage to always come back to it. However, I also think the Croft is probably quite under rated, but I love it. It has a fine phono stage built in, and really has that something special going for it tonal wise, it just sounds right to my ears, measurements and all the hubbub be damned. And it is quite a bit cheaper than Naim etc.
The Naims do have more drive, they will do well with a more tougher load, where you may have to be a bit more careful with the Croft, just my opinion there, and I don’t see it as an issue with what you currently have, provided you aren’t trying to fill a large space. Really, I enjoy both equally well, they just tend to go about things a bit differently.
You have excellent sources, and in general, can’t see how you could really go wrong with any of your amp choices, along with the speakers you have. If possible, try to get a demo of the amps, could be tough right now, but we’ll worth it to see which you prefer. Have fun, enjoy the ride, and your music, more importantly!