Just to add my $0.02
I suppose all main UK charter operators have more or less the same product, so I'm elegible to write my opinion
Flown MyTravel(Airtours) longhaul (on A330) last month in Premiar Gold and would say that it is really worth to pay something like GBP 260 per person return.
First you can do an early check-in in the eveing. Or you have a choice to join a 3-hours long waiting with everyone else in the morning.
OK there is no business lounge but it is quite understandable
Then you have priority boarding which is nice (although checked baggage with PremiarGold labels was the last to appear on the conveyor at destination!!!)
You have a welcome drink (althouth not a champagne, just water/juice) and free headsets.
Then the most important thing. I'm 194 cms tall and 105 kgs. My Travel A330 Premiair Gold is 2-3-2 layout leather seats with a reaonable (a bet 34-35") seat pitch. I fell really sorry for big guys traveling in economy because it is 3-3-3 layout (wow) and seems to be about 30" seat pitch. A nightmare really for those who are big men on a 10 hours flight.
Food and all drinks on-demand (otherwise you will pay GBP 2-3-4 per shot) are to complete the picture. As mentioned in previous posts it is like a good economy class on scheduled long-haul services plus little extra. Gbp 260 is not a small fee (I think you can buy UK-US ticket for that) but if you not pay it you will have a nightmare story to tell...