Something that I am surprised that no one else has mentioned is the fact that we, as DVC owners, are not guaranteed the ability to rent our points.
We can currently rent points to non-owners, but at the end of the day, once all has been said, and read....
We have the ability to use our points at our home resorts on a yearly basis.
We are not guaranteed the ability to bank our points, we are not guaranteed the ability rent them, and we are not guaranteed the ability to trade them (buying a resale, you are already limited on your ability to trade).
SO, when you look at using 1/3 of a proposed membership for the next few years - your plan could quickly find you with far more points than what you can possibly use in a year with your current vacation plans.
We bought enough points to bank, use, borrow for an every 3rd year (with an 11 month booking window) stay in a treehouse villa for a week 2 out of 5 seasons (we typically only travel in adventure and choice seasons anyway). However, when they reallocated the 2BR/GV/Treehouse point values - we find ourselves unable to use that formula in 2013 and forward - in any season. So we would have to do less than a week, and then borrow points at 7 months in hopes of completing the week reservation at that time.
All of that said - do not buy more than you plan to use. The commercial point renters (people who buy points JUST for the purpose of renting them out) are going to ruin things for everyone - or severely limit abilities for ALL members to use our ownership in the way that is best for each owner.
You should never buy a product with the plan that it will pay for itself when the rules and potential of that return are beyond your control. You cannot control DVC policies or dictate the rules. It's not wise for you, for your family, or for your finances.
Something to consider as well, when your family starts growing - you will want the NEWER DVC resorts that are 1BR 2 Bath. AKV, BLT, VGC and presuming they keep with the concept, the Grand Floridian Villas.
So when you look at the resorts where you would want to own, consider your 11 month booking window, and what works best for your family.