My '04 civic has 65k miles, noticing on the manual it recommends I have a coolant flush at 100k miles. The lads at the shop I take it to say I should have it done now?

 

Generally manuals show intervals for "ideal conditions" which means no temperature extremes, no stop n go driving, no towing, etc.

65k - 75k seems like a decent time to do it, although I wouldn't rush into it just because your mechanics are recommending it