You have to remember
it is still a charter flight, so don't expect first class. Having said that, I always fly JMC/Thos Cook and whenever I can I upgrade. At ?200 return there or thereabouts it is expensive, but for a long haul flight I think it's worth it. The seats are wider, you have quite a bit more legroom, seats are leather and quite comfortable, food is the same, entertainment/TV is the same, drinks are free and you get a "goodie bag" (same goodie bag coming home as you got on the way out though - never been able to understand the reasoning on that one). There are 50 seats or so in the premium cabin, so it's generally quieter - not usually any rowdy kids!
These seats do get booked up quite early, you are unlikely to get them last minute. That said, last time I travelled I got lucky on the return journey, and only had to pay an extra ?20 - bargain!