It's an emotional topic, but here's my take, from 50 years of looking at and imaging stuff:
>Messier catalogued around half of the big, splashy discrete Deep Sky targets optimized for today's ~smaller~ imagers (~up to 125mm); that is, as available from his mid-northern latitude.
>If you have a bigger imaging system (~up to 12-in)... an easy thousand DS objects become major/worthy targets of interest.
>If you have a huge system... that explodes to effectively unlimited number.
I have noticed that we here, on CN, tend to capture the same few dozen targets (90% of posted images?) over and over again. Nothing wrong with that, nothing at all! We all want to snag: Horsehead, Orion Nebl, Andromeda Galaxy, Dumbbell, Hercules Great Globular, Veil, Markarian's Chain, Rosette,...
My imaging strategy has always been to alternate comfortable familiars with obscure wallflowers... especially ones that I expect no one at all is going after. Like all those "little" NGC galaxies splashed all over the Uranometria charts. I'll sometimes look at and image a few ~just because~