All depends on how long you finance, the rate, and whether you will continue to go to WDW as a cash guest while "saving" for DVC. When we decided to buy in, we considered the financing option and when we laid it all out, it would have still made financial sense to do it. The only difference is that the break even point would add a few years. The plan was and still is to own DVC until expiration because we enjoy it as a vacation place, even now with adult kids.
We ended up not needing to go that route.. but we had a certain vacation budget that got spent every year, and since buying DVC fit into that, even with interest for the first 5 years (the length of loan we would have done), we went for it!
Prices do change so that is another thing to consider and sometimes, if things go up, what you saved in interest by waiting is actually less than what it costs you to buy for cash a few years later. I paid $73/point just 4 short years ago for SSR...its now closer to $110. For my 300 point contract, that is a difference of $11K. Even a 10 year loan at 6% comes up to total interest of $7500, a savings over waiting.
Now, its obviously a gamble because had SSR not gone up, but gone down, then you lose. In the end, it really is only something you can decide but in comparison to cash rates, I think financing isn't always a "no way" situation.