(I've missed your presnece on TF, Sammo)
I think there's a connection between "pretty tennis" and "good technique." I mean one of my favorite junior players has terrible-looking strokes, but it's efficient. At the same time, I don't really see her lasting long as a pro with those strokes (if she does turn pro).
IMO, aggressive games don't necessarily make pretty tennis because it relies on brute force sometimes and is prone to uglier UE's. So sometimes, pretty tennis isn't a waste of time...
Pretty tennis translates best on clay, though. All the stroke production, fine touch, etc., is needed most on clay. I think that's something your coach doesn't notice.