kinda in the same boat...my next jump hopefully will be a 24" from my 18". I observe with 20" and a 22" buddies.
ARPs and Abell are my main interest and the 18" is capable. My dark skies are mid- Wales, a 3hr drive where we rough camp for the weekend.
but I just have the fever and the big 50 is around the corner!...you're only here once!