At the risk of getting some angry rhetoric from a few of the above posters, I'd advise you absolutely to rescind immediately. The fact that you are asking what to do tells me that you aren't ready to buy; you have too many questions. You have only a few days to rescind but can buy next week, next month, etc.. Take the time to learn the system and the implications of buying direct versus resale.
Keep in mind that the only thing lost by buying resale is the ability to trade for points. A prior post discussed at length why Marriott is extremely unlikely to penalize resale owners wrt making reservations at their home resort, including excerpts from resort legal documents and with professional opinions from lawyer members of Tug. Various salespeople have stretched the truth a bit in this regard.
As for the future- Marriott has hinted that they will be rolling out a points program, akin to the Asia Pacific Program, which current owners will have to buy into if they choose to do so. Resale owners may or may not be offered this option. However, the ability to trade week for week will be retained and, imho, many if not most current owners will continue to trade in II and not opt to pay the $5000 or so that Marriott is currently charging to owners of resorts participating in the Asia Pacific points program. For many reason, besides cost to upgrade, I think a lot of people will hesitate to change into this system. It offers more flexibility, but severely limits any upgrades and, in many cases, 2 BR's at one resort will only have enough points to trade into a studio week at other resorts. At any extent, I expect that there will be many Marriott owners who will want to continue to exchange at least like for like and continue to hope for upgrades and, therefore, weeks will continue to be exchanged in II and resale owners will continue to be able to reserve their owned week and exchange for other properties.
Take the time to read through lots of posts. Keep in mind that most of the more ardent direct purchase buyers bought at a time when they were offered 300,00-500,000 points up front and when prices were much lower. Today, purchase incentives are down, prices are higher, and annual MF's are higher. After the most recent point devaluation, it will now take approximately 3 trades for that European trip, and the hotel vouchers have been shortened from 7 to 5 days. Points awarded for trading remain stable over time, but MF's escalate and Marriott is free to (and has) devalued points over time, making the cost of each trade more but getting less in reality.
Admittedly, there are some people here who still feel those fabulous trips that they might not otherwise spend the money on are worth it. Some evaluate the benefit as the rack rate of the hotel and of business class travel, and that equates into $$$$'s. Others feel the monetary value to them is the way they would normally travel, including staying at some great properties but at discounted rates and taking the less classy and less comfy coach seat route. That's a decision you have to make- but you need the time to make an informed decision.
As for which property- Both are terrific properties. Admittedly, I am partial to Aruba; others favor St. Kitts. As for trading- I think Aruba Gold is a better trader than Gold St. Kitts. Because it is below the hurricane belt and has basically the same climate year round (like Hawaii), Aruba is really a year round destination. Heightened winter desirability is not because of better weather in Aruba at the time, but because so many people, esp. from the Northeast, want to go to the Caribbean from mid-Dec. through April. Last year someone posted various evaluations that Redweek gave to a 2BR July 4th week at many of the properties, including the Hawaii ones, and Aruba Surf Club weeks were number one.
Again, if you decide to rescind, make sure to follow the instructions exactly. Remember rescinding doesn't mean you can't buy directly- it just gives you the time to decide how and what to buy without the clock ticking. Feel free to ask questions along the way- and welcome to Tug