Buying used: Parasound A21 or A21+ ?

I’ve owned  an A23+ for the past year. Im using the preouts of a Yamaha flagship receiver in a 5.1 professionally calibrated system for audio and video. The Parasound is one hell of an amp! I can’t find any fault at all in its sound. It delivers plenty of power into my 4 ohm speakers. It’s damned near perfect for home theater AND 2,1 channel audio with Vinyl LPS as the source. I got curious about these new Class D Gan amps and bought a powerful one. The Parasound crushed it! It’s more visceral, dynamic, better midrange, tighter bass, tonality, etc. The only area that the Gan amp matched was soundstage and a clean high end. Toes just weren’t tapping with the Gan amp. It was lifeless in comparison. I put the Parasound back in and the smiles returned.

i will be putting a silver a21+ up for sale soon.

I have a similar dilemma: I'm looking to upgrade my Linn Majik 2100 amp to something in the Halo line, but can't decide between the four available options - A21, A21+, A23, A23+. I'm currently powering Monitor Audio RS6 speakers, so I imagine that any of the four amps will have PLENTY of power. The two questions are:

1) I'm thinking to future-proof a bit in terms of going up to A21/A21+. I haven't put much thought into what speakers I might upgrade to, but likely won't be anything too exotic or hard to drive (maybe B&W 702 S2, Focal Aria K2, SF Lumina III, Spendor A4/7, etc.). Would I be going overboard (nearly doubling the price) with A21/A21+?

2) It's not clear to me from reviews, technical literature, etc. how big an improvement the "+" version of either model improves over the older "non+" version. Do I really need to spring for the newer "+" version or will the older version be completely sufficient/satisfactory? It seems that at least the A21 has stood the test of time quite well, so it's hard to imagine I wouldn't be pleased with it.