If you decide to cross the bridge, you will get a whole new vibe. St. Petersburg has variety of options, including walking the pier, bar hoping or bike riding through the town. You may need more than a day to fully experience all that St. Petersburg has to offer. You must try Annata's steamed mussels if you decide to visit.
Obviously if you're in Florida, you must visit America's #1 beach. We live on the gulf coast, so you have about 20 miles of options, depending on what you're looking for. Clearwater beach will be more lively, tourist everywhere, and lots of food options. Madeira Beach is more family friendly, is typically quiet and has great ice cream shops. Pass a Grille beach is where you go to get away from everyone, and to soak up some sun in peace and quiet.