I had the NAD C370 integrated in a prior "B" system so I know the NAD unique sonic signature with the strengths and warts of that NAD sonic signature very well.
Ignoring the 3020's very modest power output capabilities, its sonic signature is definitely not for everyone (at a minimum) ... full stop.
You may have an unscratchable nostalgia itch to buy the 3020 budget amp, ....fine .... but IMO don't sell the REGA amp first before you go down that road. There is high likelihood that in an A-B direct shootout comparison, you may regret it badly.
As highlighted before, "vintage" in audio is not the same as in wines .... they are just old techology nostalgia kit that dont compete well with current technology, the don't improve with age, and they demand extensive and expensive refurbishing that takes the shine off the new toy quickly...its only a question of when.
Those costs frequently take it out of the realm of "is it worth it?' plausibility and disappoint mightily - full stop again.