I have done a couple short cruises without ever dining in the MDRs. We did some room service and some quick service. The food choices aren't as elaborate, but I've had 2 hour dinners in the MDRs before and that isn't how I want to spend my time. Since reading the forum, I've decided to ask for my own table and to try to speed up my dinner service next time. We get full and don't want dessert, so hopefully that will help, too.
For room service, there were things I asked for that were not on the menu and they said yes they could bring it to me. I know a bowl of fruit was one thing I ordered at dinner once, but I can't remember what else. They came extremely fast both times, but we were on the Wonder.