If you're taking a Disney vacation, it just seems to make sense to make it ALL DISNEY by staying in a Disney resort. I have stayed off-site at some beautiful places, but it still isn't the same as being a Disney resort guest. There are little perks to staying at the Disney-owned resorts, as I'm sure you know, but really the best part is just being immersed in the Disney magic for all the days you're on vacation there. I guess if WDW were just another amusement park, it wouldn't matter so much where you stayed at the end of the day. To me, however, WDW is really a vacation destination -- and it just makes sense to stay in one of the on-site resorts to fully appreciate it.
Anyway, having said all that, I also should add that I don't think Disney is all that outrageous price-wise in terms of hotel accommodations. To me, the pricey thing is meals and souveniers!!! If you're going next January during value season, the prices are the most reasonable of any time of the year. You could stay at the All Stars for about $60 a night or one of the moderates for around $90 a night, which to me doesn't seem prohibitively high at all. Granted, these are not Disney's deluxe hotels, nor do they have loads of room, but you'd definitely be immersed in the Disney magic and be able to take advantage of the privileges of being a resort guest.
These are just my opinions (for what they're worth!), but I really do believe that it's extra special when you stay within the resort during your Disney vacation... As I say, I've done both and now won't ever go back to non-Disney properties during our family trips -- guess I'm spoiled!!!
Have fun planning your vacation,
Sarah