Some basic information you may need to consider:
70's Nishiki International 10-speed
Right now I have:
Rims - Sunrims CR-18
Wheels - Vittoria Zaffiro 27 - 1 1/4

I've put a little over 1000 miles on them both, and want to get some better tires, and have been leaning towards Schwalbe Marathons. which they do have in 27s, online.
Would it just make more sense to upgrade to 700s so I'd have more tire options and wouldn't have to order them online again in the future?
My thoughts are, that the rims are still just fine, and should have many more miles to go on them, so spending money on new ones just seems excessive right now. but, it might be for the best.
Right now, I'm mostly just commuting around campus and around town, putting in roughly 5-10 miles a day, but I want to tour more as well.

Thanks for your help