I met a group of contiki travellers about 3 years ago in a bar; they said it was just one giant piss up; the people I've spoken to over the years who have also done it agree with them.
I looked at their website and couldn't believe the prices...Some people are making some serious cash there!!
For example; theres one in South America for 36 days that costs just under £7k..............
For £7k I'd expect to stay in South America for 7 months and do everything that is listed on their itinerary...
Another one in 25 days that costs £4k in Mexico and Guatemala...I spent 3 months travelling in Mexico and spent just over £2.5k and that was when the Peso was stronger than it is now!!! I also spent money on Spanish lessons, a huge festival etc etc. Given the exchange rate of the Peso now I'd expect £4k to last the whole 6 month visa allowance.
I'd steer clear of them as for me I think it is a hugeeeee rip off preying on people who aren't really experienced as travellers or people who like one of my Brazilian friends only had 2 weeks of work so it was perfect for her.
If money isn't an object then go for it.