I think this past year's storms had a pretty significant impact on St. Pete Beach. It felt like damn near 50% of the resorts and restaurants on both sides of Gulf Blvd were closed and/or under construction. I still was not very impressed. The resorts, restaurants, bars and stores on Gulf were all pretty run down. The main strip was not very walkable. Narrow sidewalks inches from a busy 5 lane highway with people doing 50+. No beach walk on the beach side. I wasn't expecting a ton and with the time and budget I had to throw the trip together, it was as good as I could have done, it just didn't really measure up to some of the other places I've been. I can't really speak to Destin as I said we spent most/all of our time there in the resort.
St. Petersburg itself surprised me in regards to how nice it was, but I wouldn't really call it a beach town, either.