1. Why do you have to buy at Saratoga Springs if you can use your points all over?
First, this question applies not only to Saratoga Springs but also the other DVC resorts (those sold via resale as well as those you may be able to buy through Disney). When you purchase DVC points you don't just buy the points you actually acquire an interest in a specific piece of real estate for a specific period of time. In effect under the DVC system you are leasing that piece of property for a stated period of years.
With respect the issue of points usage. In the DVC scheme of things the advange of owning a real estate interest at one property over another is has to do with the 11 month vs. 7 month booking window that others have described. The 11 month window can be important if you anticipate traveling at peak time periods and if you want to stay in certain resorts other than Saratoga Springs. For instance, if you think you might like to go the DVC Wilderness Lodge Villas at Christmas if you own at one of the other resorts you would have to wait until the 7 month window which could mean you would not be able to make a Christmas time reservation at DVC's Wilderness Lodge (although from what I have seen on the boards you can "waitlist" and the waitlist often comes through but this isn't something you should count on).
So, if you think you would prefer staying at one of the other DVC on-site or off-site properties you may want to consider having your name put on the waitlist to buy through Disney or consider buying a resale. Only you can determine which resort you prefer and what you expect your travel habits to be now and in the future. I say put some real thought into this because if you don't you could be disappointed with having to deal with the 7 month window. On the other hand, if you are likely to travel at off peak times, or you are very flexible then it seems to me that most people claim that they eventually get what they want by using the waitlist approach. Decisions, decisions, decisions.
2.Can anyone give me positive or negative feedback so I can make a decision.
Wow, that is a loaded question and it could take some time to answer fully. First, don't make an impulse buy, really think about this and make sure you and your spouse are in agreement. Second, don't put yourself in debt if you can't afford the extra debt. Third, if you are already going to Disney once a year and you are staying on property in a moderate or better resort DVC could (I stress could) be a good deal for you in terms of upgraded accommodatons. Remember while you may indeed save on the cost of your accomodations you may find youself actually spending more because you can visit WDW more often. Fourth, if you don't really love the WDW experience well DCV may not be for you.
In our case, we really love the WDW experience and we were going at least once a year staying in moderate or better resorts. It took us 3 years to decide the get into DVC. We have no regrets over waiting, it was the best decision we could have made but of course this worked for us and I am in no way suggesting that this is the best approach for anyone else. I can't think of any negatives at this point and we've owned for 3 years and taken about 8 trips over that period. We've stayed at BCV, HH, WLV, and BWV and each has a different charm plus we liked them all. We have a preference but it's not important for this discussion.
You will find that most people who post on these boards have a very positive attitude about DVC. Yes, there are some who have gripes from time to time (housekeeping has been a recurring issue from time to time). Read the boards, ask questions, think about it and hash it out with the spouse. If you do these things you are likely to choose wisely.
3. I was told I have 72 hours for some incentive program they have.
We were told the same thing when we first got interested but when we finally decided to buy we still were able to take advantage of the incentives. But, there is no guarantee that the incentives they are offering now will be in place should you decide to wait. Still, if you feel like you've read enough, discussed your individual situation thoroughly then by all means act within the 72 hours.