It could be worth it. However, alot depends on your vacation habits. If you currently stay offsite when you head to see the mouse, then there is no way the costs of DVC will ever come close. However, if you stay onsite at moderate or deluxe hotels, then that makes the decision easier. Th current buy in at SSR is approx $16,000 for 150 points (It is actually a little less, 15,000 and some change, but I rounded it up). You get these points for 48 more years, so the buy in cost on these points are $2.22 per point (I took 16000 and divided it by the number of year left to get the annual total buy in cost and then divided that by 150 for the per point buy in cost). You then also have to add it the annual dues which vary per resort. I will use $4.00 per point as a round figure. I think SSR is slightly cheaper than that, but I am just trying to give a general example. So for each point you spend, your cost per point is approximately $6.22. The next factor is determining the number of points you will need for your vacation. With a family of 6 you most likely need a 2 bedroom unit. A 2 bedroom unit at SSR is 36 per weeknight during the summer season. Holidays will be more points and there are also other seasons which are less points. Weekends points are usually double the week day points so most DVC owners avoid weekends like the plague. So, 36 point time 6.22 gives you a cost for that unit of $224 for the night. For the price you get a full kitchen, 2 bathrooms, washer dryer, jacuzzi tub, room to spread out, 3 television (my favorite with 3 kids).
Now, some other factors to take into account is that if you finance your purchase, your buy in cost per point will be much higher. Also, annual dues will more than likely increase, as do hotel costs also, so that can be a wash. Also, by tying your money up in DVC, you lose the benefits of investing that money elsewhere. I am not into those kinds of forcasts, so I can't really give examples of that, but it is something to seriously consider.
You can also consider purchasing points on the resale market. Be aware though that the other resorts only have 42 (I think) more years left.
Lots of things to consider. Hang around the DVC boards and you'll get lots of information.