Premium and platinum are not dining plans, they are all inclusive vacation plans and as such cost a great deal more than simply adding the deluxe dining plan.
These packages also include unlimited recreation, most tours, and tickets to Cirque du Soliel. They also add Portobello Yacht Club and Fulton’s to your dining options and dining itself is equal to deluxe dining with app, entree, dessert and beverages 3 times a day, plus 2 snacks and beverage cup (2 credit signature/show rules appear to not apply). Finally the park tickets are essentially ultimate park hoppers allowing access to waterparks and Disney Quest and unlimited park hopping.
When you step up to platinum, you are essentially stepping up to concierge/club level pre-planning services. You also gain Victoria and Albert’s, spa treatments, and room service (as long as you’re staying in a deluxe resort), in room child care, reserved Fantasmic seating, preferred fireworks viewing areas, and fireworks cruises.
Ariel, these two are clearly far beyond your budget.
You have until three days before arrival to upgrade your reservation to add any vacation package to your existing reservation, although with your being in the UK, I’d probably make all changes no closer than one week out. If you are going to do this, I’d make your initial reservation deposit only equal to one night. The reason is that when you switch, they will have to charge the entire new reservation if you’re inside 45 days of arrival and will then credit back your original deposit to that credit card, which can take as long as 5 business days.
The current plans are
CS or QS (quick service or counter service)(entree, dessert, beverage)
2 CS meals, 2 snacks, resort refillable beverage cup, around $32 adult/day
1 CS (entree, dessert, beverage), 1 TS (entree, dessert, beverage), 1 Snack, refillable cup, around $47 for 2010
3 TS (appetizer, entree, dessert, beverage), 2 snacks, refillable cup, around $72 for 2010.