And as for wearing or not wearing jeans to the theatre...
I wear jeans. But I didn't used to. For me, it's mainly a matter of the time of year I'm going. And since I usually see most of my theatre during the winter - at least in NYC, I dress more to stay warm than to look good and/or appropriate. Jeans are warm. Dress pants are not. However, I do wear nice jeans. No rips or tears, not "washed" out. And usually black.
Otherwise, I usually opt for a nice pair of black or dark blue chinos.
Now, if I'm going to some place like the Metropolitan Opera or some special event at the Kennedy Center, then I put on my one and only navy blue blazer. -Plus the requisite dress shoes, socks, pants, belt, shirt and tie, of course!