I thank everyone for their prompt posts. I've requested information from Delta once or twice via email/form over the past few days. The one response I received did not answer my question. The CS rep pointed me towards out-of-date airplane layouts that made no mention of whether armrests can be raised. The layout maps were identical to the ones on seatguru and were not at all similar to the ones you pull up when actually selecting your seat at Delta.com. The CS rep did impart some useful information about CRJ planes that I thought I'd share here. There are only 3 seat belt extenders for each CRJ 50-seater while the CRJ 70-seaters have 5 each. I guess I'll need to get to the airport extra early to put in my request for an extender.

Thanks again for all the helpful feedback. I hope the legs of my trip that involve 757s is slightly more comfortable.