I am currently running stellarmate on a p4, 4gb, but I managed to secure an order for a pi 5 8gb.
My setup is an open astro tracker, open astro guider, asi183mc pro, and a DSLR lens. I dont usually VNC into the stellarmate system, rather connect to indi remotely with my PC/Laptop.

Should I move my stellarmate system over to the pi5, or reserve it for a more demanding application?

No harm in trying it, but I have feeling for you, there won't be much of a difference. Interactive application performance should be better on the 5, but as you said you aren't doing that. The wifi is still AC. The only other thing I could think of is getting the NVME adapter and adding a real NVME drive instead of an SD card. This should improve everything to a noticeable degree. That being said you could boot from a USB 3 SSD drive now on the pi4 also for a stability/performance boost.

If it's workng well Id find something fun for the Pi5 Just my .02$

Good luck.

Bryan

Oh one other thing. The real time clock on the pi5 could be useful also.