I find SD adequate for most movies produced on film. Digitally produced movies with lots of CGI do look much better in HD so that's where I'll make my choice.
For TV shows, I'm not a die-hard HD fan so I can often live without it unless it's for my favourite shows and I expect to keep them in my library.
The bottom line is, fortunately, I can afford to not be cheap. If I want to watch something, I'll rather pay for convenience so tv is perfect.