Sounds like fun to me.
I bought a year-old used go cart for my boy and girl (and me) about this time last year. It is a two person cart and my wife and I can (mostly) comfortably ride in it). It has a full cage and seat belts, too.
Mine has a Subaru/Robin engine. I have read some good things and some bad things about it. I've had great luck. It starts and the first or second pull everytime and runs great. The only problem I've had is finding a replacement fuel cap (my boy put in some gas and didn't tighten it, so it fell off). I finally found one, and I'm going to put it on a chain so that doesn't happen again.
The only real bad thing that has happened is the rear part of the frame (where the engine mounts) broke in 4 places due to too much hot-rodding (i.e. jumping gullys and rawhidin' too much). It cause the 60 tooth sprocket to get mis-aligned, strip a drive gear, throw the chain, etc. I finally got it all welded and re-inforced (good enough I hope; I'm a pretty bad welder). I will have to say that I'm surprised how thick the frame tubing was. I only burned through in one spot). Anyway, I got it all back straight, and it's ready to go....except when I put everything back together, I lost some pieces out of the clutch, and now I'm waiting for them to show up.
It will last a lot longer if you can get 'em to take is slow...but it's not as much fun. Good luck and take care.