When we went on the trip there was one guy on his own and he got on with everyone, so I don't think it was too much of a problem as you are always in a group. Best thing to do is to start speaking to some of the people around you and then you're not uncomfortable at meal times or when sharing a 4x4.
We did the Sahara Explorer Trip, Nabeul Market and Pirate Ship. The Sahara Trip takes you to various spots around the country like El Jem (Small Colouseum), Matmata (Cave Houses), Salt lake etc. You can only see the Sahara if you pay extra for a camel ride! My advice here is if you really really want to spend half a hour in certain locations, then the next 3 hours on a coach and a not so good night in a cheap hotel then this trip is for you. For me, in the 2 days we spent about 18 hours on the coach! I'm 6' 6", so it was a bit of a pain. If you go look at how much rubbish there is out in the countryside, there is plastic everywhere!
We went to Nabeul Market on a Friday, it's not a traditional market as advertised, but a tourist market, but prices are a lot more reasonable. Get there early because by Noon seven hundred coach parties turn up and it gets very cramped. We shared a taxi with another couple for 20 Dinars return, which was cheaper than booking with the rep and we could leave when we wanted (Trust me 2-3 hours is the most you want to spend there).
The priate ship was a good experience and they do a great job of getting people up to dance etc. The pirate ship cost us £12.50, but if you are in Yasmine Hammamet it may be cheaper as we had to travel from Hammamet.
If I can help anymore please let me know.