I did the tour last summer as part of a promotion. Honestly it depends on when you are going. When we were there it was packed! 1.5 hours for everything! At the point the tour was a must. At low attendance times the park can be done in one day no problem, although I do think they have a SeaWorld type of offer where 2nd day is free.
The problem is staying in Tampa. Busch Gardens is located in a horrible part of town; really BAD. Liquor store, pawn shops, etc. all across the street and surrounding. Hotels nearby are awful. We had to drive 30 minutes to the downtown area to find a restaurant in an area we felt safe.
My suggestion. Get there, guage the crowd and then sign up for the tour. There was still availability our day. Weekends are generally bad and in the Summer they have a later night program that attracts the local kids.
BG is nice, you will be put off by the area surrounding. It's not Disney!
. I looked into staying at the Loews hotel in St. pete but once I got the map out that was NOT an option! LOL! ( "tampa hotel" my foot! 
this hotel is about 40 miles to Busch Gardens one way ) 
) Get a towncar from disney to BG. I am assuming that the rates will be pretty close to that of disney/stanford airport. please correct me if i am wrong. I understand what you are saying about just showing up at the park and see how crowded it is that day, but I just cant leave anything to chance! My luck it will be totally packed because we are going in october and BG has HOS going on at night. The tour is going to be 8 hours long, and this really appeals to us! FOTL is the only way to go. Any suggestions/tips/discounts would be greatly appreciated!
