Save your money and get a cabin higher up on the ship.the lower cabins on decks 1 2 and 3 are small,dated and look like old 70s caravan interior,well worn formica teak furniture.drinks package does not include bottled water,thomsons own wine is cheap plonk, not sure about the beer.if you want a better wine or beer you will have to pay a subsidiary charge 1.50 for lager and 8.00 for wine so beware.lager is 3.00 a pint wine 3.00 a glass.work it out how much you drink,you will probably find it cheaper to go it alone.the ship vibrates so much you will probably think you are drunk anyway.
When I booked with Thomson they wanted the AI upgrade money when I booked. As I reckoned I could not force down over a hundred quids worth of booze in 7 days I did not bother. Next summer the Celebration is doing Greece etc and I got a free AI upgrade for that trip!. This summer Celebration is cruising to the Baltic etc and there are no AI upgrades available, I think because of the danger of 'booze cruise' attitude among the passengers.
I think the general opinion is that it is cheaper to pay as you go rather than pay for the all inclusive. Obviously its very nice to get the all inclusive free as we did for our 2 weeks on Calypso starting on Monday!!!! We booked last August though and just caught the special offer before it was due to run out.
I think you can only book it BEFORE you go and not when you get there - you would have to contact Thomsons or your travel agent and ask for the upgrade before you sail and pay the all inclusive drinks rate. Unless you drink alot it may not be worth paying for. If it is free or the £30 cheap offer upgrade it will be worth it - at £150 per person per week ( the typical full / normal rate ) it probably is not.
If you like to chill out and enjoy yourself on hols (which is the general idea) i'd opt for the AI upgrade - I found it great value for money - to compare, i've been on the spirit with the AI in 05, then on Island Escape in 06 without the drinks package and our bar bill between three of us for the week was £700 - fair enough we did enjoy ourselves :-)
I'm just back from being on the Destiny and again went for the AI - its the way to go.