well having looked at club meeting nights at the difference between a whole bucket load of telescopes i can tell you one thing the difference between a 6" dob --> 8" dob is big. same with a 8 --> 10" but the difference between the 10 --> 16 floored me. Taranchula neb is like picking a spotlight out of a dark field. and faint faint fuzzies aka Ghost of Jupiter shows detail. Eta carina has colour ect ect even orion was starting to change a bit in colour not its normal blue hue.
If your not planning on photography then let the aperature virus run loose get the biggest baddest piece of machinery you can swallow!
I guess the only thing holding amature astronomers from going bigger than say 10/12" for photography is mount costings! when you look at 10k+ for a mount, and 5k+ for a piece of reasonable kit, its not cheap. but in also saying that CCD's/DSLR's are so sensitive you don't need aperature as much.
thats my 2 bobs worth and logic for you to chew on.
