You can stay 'almost' anywhere. I'm sure you know a lot of this already, but I'll just recap.
When you buy
DVC you purchase a real estate interest in the Disney Vacation Club. Currently this includes 3-locations at WDW (Old Key West, Boardwalk Villas, and Wilderness Lodge Villas, (with Beach Club Villas due to be added late next year)). Outside WDW it includes Hilton Head, and Vero Beach resorts.
Unlike most timeshares where you purchase a specific unit for a specific week each year, in the DVC program you purchase points which are then 'spent' for accommodations. The number of points required depends on the resort, the season, and the room accommodation types.
Point charts are provided which show the 'costs' in points. Using points at any DVC resort is the prime purpose of the program.
Additionally, they have several exchange programs available. Called the Disney Collection, you can use points to stay at other Disney properties. At WDW these include GF, AKL, BC, YC, Contemporary, Poly, Fort Wilderness, CB, CS, and PO. Note that there are no value resorts (All Stars), nor is Boardwalk or Wilderness Lodge included as they have their own DVC villas attached. (Also most likely, when the Beach Club villas are completed, it is expected that BC and YC will be removed from The Disney Collection. You didn't ask, but also within this collection are three
Disneyland hotels, four Disneyland Paris hotels and 3, 4 or 7 night cruises on
Disney Cruise Line.
After the Disney Collection, there is the Concierge Collection which includes resorts all around the country. There are currently 30 resorts listed in the Member's guidebook. Examples include the Grand Hotel at Mackinac Island, or the Kapalua Bay hotel, Maui, and so on.
Next is the Adventurer's collection. This includes backroads biking trips, rafting trips, African Safaris, or Alaskan Cruises.
Finally, like any timeshare, you can trade your Disney points for other timeshares around the world. In this case I believe you actually commit enough points for a specific Disney villa, and this is then exchanged through the external programs.
Various fees apply when doing exchanges outside the actual DVC properties. I don't know for certain if fees apply to WDW hotels or not.
To answer your other question, for comparison, a 1-B/R villa at Disney's Villas at Wilderness lodge would require 22 points weekdays - low season, 45 points weekends, or 40 points weekdays - high season, 75 points weekends.
Using your points for a Poly Concierge room would be 48 points, weekdays - low season, 86 points weekends. For high season, it would be 68 points weekdays, and 122 points weekends.
If you wanted a 2-B/R unit at Wilderness Lodge villas, for comparison, the points would be 30, 60, 50, 106.
As you can see, in all cases, you can get a 2-B/R unit for fewer points than you could get Concierge at the Poly.
Even garden view rooms at the Poly are 31, 56, 48, 86 points respectively. This is more points for a regular hotel room than a 1-B/R at Wilderness, and in most cases, more points than a 2-B/R unit at Old Key West resort (22, 54, 41, 100 points respectively)
This is why most DVC'ers feel that the best 'value' for their points is to use them at DVC resorts. Very often you can get discounted regular WDW hotel rooms that makes it more economical to pay cash if you want to stay there, and save your points for DVC accommodations. Of course, like anything else, there are always exceptions. (Sometimes using points for a
Disney cruise is a good deal, and other times paying cash is the better deal. You just have to compare.)
Just for final information, if you use points in other than a DVC resort, then DVC will rent the unit you are not using (Studio, 1-B/R etc at one of the DVC resorts) out for cash. That cash is then used to pay the participating hotel for the accommodations they would be giving you, such as a Polynesian Concierge room. This is how that part of the program works.
Note that DVC has 5-seasons while the regular WDW hotels have 4-seasons, so you would actually need to compare on a date by date basis to determine actual point differences.
Hope all this helps.