I know that theatres have to market themselves aggressively. It's a tough, competitive business. Hell, I'm a marketer myself, so I respect good marketing, and I even have a higher-than-normal tolerance for mediocre marketing directed at me.
So if I've performed in one of your shows, then by all means, put me on your list -- e-mail, snail mail, whatever. I like you and want to keep up with what you're doing.
If I've auditioned for a show of yours and didn't get cast? Well, put me on your list. I'd probably come see the show anyway, because I typically do go see shows I don't get cast in, but it's nice to get a reminder.
Now if I auditioned for you several years ago and haven't seen you since, you ought to think about pruning your list a bit.
Finally, if I've submitted my headshot to you one or more times, and you've never so much as called me in for an audition? Fuck you. Take me off your list. Don't even add me to your list in the first place. Seriously.
Of course I don't expect people to call me in every time I submit or even any time I submit. That's totally their option. And I'm fully accustomed to rejection. But when you add me to your list, it looks suspiciously like you were just collecting names for your marketing and not really holding a legitimate audition.