Lori, I did a day trip from Coimbra by bus to Nazare. I love trains and dislike buses and looked into taking the train for sure (from either Lisbon or Coimbra), but it was just too much trouble. Too many connections. The train doesn't even drop you directly in Nazare anyway; you need to take a local bus from the station into Nazare. The bus from Coimbra or Lisbon is direct. As much as I was not looking forward to the bus ride back and forth, for a bus it was comfortable enough.
I loved Nazare, and I have several friends who visited and also enjoyed their visits and would recommend it, even though it's a bit tacky-touristy.
If you are staying in Lisbon, you can certainly take trains for the day to say Sintra or Cascais if you just want to ride a train somewhere.