I haven't been to Port St. Lucie, but the Washington Nationals (and before them the Montreal Expos and Florida Marlins) spring train down the road from me. I go to one game a year, DH goes to more (all the games that the Mets travel here for, plus he is taking DS to see the Cardinals). My suggestion...lots of sunscreen. It's usually a fun, relaxed day. Enjoy.
I wish we could go... the Cardinals are in Jupiter but we can't go to FL this year for spring training. We were there for DH business in January and WDW in May so no Cards this year.
We will be in Juno Beach to see the Cardinal from March 6-12. This is our first Spring Training trip tho we have season tickets for the Cardinals in St. Louis. Sounds like a lot of fun!