Hi there, the dues (annual charges) are so many £s per point, so you pay more £s each year if you have more points.
You can save a lot of money (over time) if you usually would stay in a moderate of deluxe resort. Dh is an accountant and thinks that it will take us about 10 trips before we start saving money, because we varied between moderate and value resorts in the past.
We save a little money by buying in some food (you can pre-order it and have it delivered to your room before you arrive) and eating breakfast and some lunches in our room. This only saves a little - but every little counts in my book.
There are some discounts - 10% off UK
disney store, and 10% off some restaurants at WDW but these are a bonus if you have DVC and not enough to swing your decision.
If you have to borrow a lot of money to buy DVC then I would say not to do it.
Definately do the tour when you are out there, and make a decision when you come home and the magic fades a little, so you can make a rational decision.
Oh yeah, you only get your rubbish taken away 1x a week, rather than every day and you don't get your beds made up at all. So if not having any 'house work' is important to you on holiday, then you should bear this in mind too.
Hope this helps