I was thinking of getting a used one to map out the cellular coverage of my area (Gainesville, fl) because it is so terrible (along with wardriving). Does anyone know if this is the right tool or if there is something else more appropriate.
No, it's not. The cell sites use a control channel, and the different cells use different frequencies. They get reused occasionally, but not on adjacent sites.
You could find a control channel, and see what the coverage is for a specific site, but it won't hop between sites. You need a cell phone in "field test" mode to do that. You can google your cell phone model and the term "field test" and you can often find directions on how to put your phone into this mode. I can do it with my AT&T iPhone, and it will spit out the cell site info, along with the signal strength in decibels.
Also, a cellular carrier won't really be interested with this information. It might satisfy your curiosity, but the data won't do much else for you, and it won't do anything for the cell carrier. The carriers only care about profit, and if they don't see a profit in improving coverage, they won't do it. Won't matter how much data you provide. What they want is a reliable customer base in that area to make the investment worth it. You can certainly call and complain. It won't hurt (much), but don't expect them to come running out and install a new site.
Also has anyone had any experience as to whether the 3G/4G boosters/repeaters actually work or if it is just a gimmick. If they do I plan on hooking one up to a high gain 3G/4G larsen or laird antenna..
Depends on which ones you get. Cheap Chinese e-Bay ones are going to be a mixed bag. A decent one, like a Wilson, will work pretty well. I used to have one in my truck. It was a Wilson mount that held an iPhone, so no direct antenna connection to the phone. I had an NMO antenna permanently mounted on the roof of the truck. There were places I could go where the cell phone on it's own would not connect to the network. With the Wilson unit, I'd get 2 or 3 "bars" and have no problem making/receiving calls. AT&T was the carrier.
I have a direct connect Wilson that we tried out with one of the call boxes at work. Again, AT&T was the carrier. I installed an NMO mount on the top of the call box, and this amp inside. The call box on it's own would not connect reliably to the network. The Wilson amp helped slightly, but still not a reliable connection. Ended up switching to a Verizon radio and got it all to work just fine.
I've never been really impressed with the Wilson gear. Their antennas are pretty crappy. The iPhone adapter I had worked well, but the housing was really cheap plastic, and the mount was utter and total crap. Had to rebuild it with a "real" mounting. I got rid of the whole mess a few years ago. Sold the amp and antenna (with a mag mount) on e-Bay.
The direct connect unit seems to be built well, but it didn't accomplish the task. Not because it didn't work, but because the AT&T coverage was too crapy.
That is the part you would need to consider. It isn't just about boosting your transmitted signal, you also need to amplify the incoming signal from the cell site. If there isn't enough signal there to overcome the noise floor, no amount of consumer grade amplifier is going to fix it.