I didn't get to Evora on my trip to Portugal last May. I did spend a few nights in Coimbra on the way north from Lisbon to Porto. I'm guessing Coimbra is far less touristy than Evora. in fact, Coimbra isn't touristy at all, and that may be a nice break from the tourists in Lisbon (but will it be busy in March? Not sure.).
Coimbra is pretty small. The university at the top of the steep hill up is very interesting. During the 1930s, the fascist dictator Salazar, who had been a professor at the university, expanded it and left behind some ugly fascist architecture - big, outsized buildings - along with some of the much older buildings you can see during the tour. I think you'd really need to like universities to have this make it worth a day trip from Lisbon.
You might also consider a day trip to Tomar. I stopped here for a few hours off the train (more of a detour than a direct stop off the train) on the way north from Lisbon to Coimbra. Tomar is a little more charming and even smaller than Coimbra. It lacks the big university, but there's also an old convent on the hill above the town. I hear Tomar will be added to the next Rick Steves Portugal book, so soon it will probably be mobbed with tourists. Last year, not so much.
One of my favorite stops was to Nazare, a beach town in central Portugal (and an old favorite or Rick Steve's). I did it as a long day trip from Coimbra by bus. You'd also probably do it by bus from Lisbon. Perhaps at the end of March the town will be pretty dead, but it's worth a last-minute diversion based on the weather. Nazare is a tacky tourist beach town in once sense but also very unique. It is included in one of the Rick Steves Portugal videos - you can watch for yourself to see if you think you'd like it. I love the ocean so it was a must for me.
