Check out my link, Gary:
indilib.org/forum/general/6922-kstars-on...ate-20-04.html#53293
I am extremely happy with my RPi4 setup at the moment, in fact, haven't been going back to my ZOTAC pico332 mini-PC in a while. That works fine, but it has other issues the RPi4 does not have and vice versa.
With the new Ubuntu MATE 20.04 installation, KStars immediately ran fine and without a hitch and much faster than before. A full night of imaging from the scheduler, ~800 frames, with automated meridian flip, autofocus every 60 min, everything. Could not be happier.
The problem with your SD cards most likely comes from different quality and speed. I am currently running my Pi4 with a SanDisk 32 GB card which has the OS and astrometry files, and I am saving all images to an SSD. Those downloads happen in an instant of en eye.
Right now, I see no reason to change to a NUC or other forms of mini-PC, except perhaps at some point to one with more memory. But as far as KStars is concerned, no reason, really. The RPi4 does a stellar job for me right now.
I would stay with the RPi4 and build a system around Ubuntu MATE 20.04.
Jo
PS: Wifi 5GHz running at 433 Mbps, so control via VNC is virtually lag-free. And that is with a Wifi extender (!) and ~ 50 feet from the extender to the RPi4.