Here is where I see a potential problem.
Disney is expensive. Even with the room 'paid for' its an expensive trip. In the blink of an eye (especially in timeshare terms) that one baby will be three "Disney Adults" - look at the cost of park tickets for your kids when they hit ten. Airfare - if you need to fly - gets really expensive - we travel so much less with kids than we would if we only had to buy two plane tickets.
DVC locks you into Disney. You like to travel - for most people that involves variety. When the kids are little, Disney is the perfect vacation. But as they get older, you probably want to share more of the world outside the World with them. DVC is not a good trading timeshare.
If you hadn't put in "I doubt we'd be able to go once a year in a Deluxe resort without DVC" then I'd say "well, maybe these are the sort of people who don't have to worry about opportunity cost - they won't see a budget hit with three kids that are over ten and airfare for a family of five.
This is my deal....my husband and I make a lot of money (actually, I just quit a six figure a year job to stay home with two teenagers - and he still makes a lot of money - enough that we don't miss my income on a day to day basis - he switched jobs and we didn't loose that much) And with two teenagers - airfare and park tickets for two teenagers - two teenagers heading to college in the next five years, and a house built when the kids were babies that is now entering into "residing, recarpeting, reroofing" age - I'm not sure that we can afford DVC. We also like to travel - and right now, DVC feels a little more like a millstone than a treat, because we have these points to use, when we'd rather take the kids to Europe - and we can't do both in terms of time or money. I promised a trip to our godchild - who is a toddler and really too young - otherwise, I think I'd sell - but I'm renting out next years points and the family isn't going to WDW (we are going to take a
Disney cruise - which was FAR cheaper with cash than points). We've only ever owned enough points to go every other years - so we have gotten to take the kids to Europe because every other year has let us have both time and money to do so (and Mexico, the Caribbean, California, Washington DC). And there are expenses I didn't foresee. My mother in law is getting very expensive as she gets older - she's never had a lot of financial sense, so she has no savings - and my husband has decided to supplement her meager social security income so she is comfortable.
Look long term - where are you going to be ten years from now? Look at opportunity cost - ten years from now, will you still want to be going to Disney every year. What are you going to give up - both in terms of time and money, to go every year? Don't forget to add in the cost of transportation, food and park tickets in your planning. I'm VERY conservative financially and where I feel secure is at a different place than most people - but think about whether you will be comfortable with this long term.