Welcome to Tug, btw, and congrats on coming here before buying directly and possibly regretting it.
I totally agree with all of the above posts, especially with the take your time and read lots of back posts on this Board. A few questions to keep in mind while making your decision:
-what is your family composition and will it likely change? Do you need a studio/1BR or do you need a 2 BR, and what will you need 5 or 10 years from now?
-when do you anticipate traveling? Are you restricted to school vacations or do you have flexibility and, again, what about 5 or 10 years from now?
-what is your job flexibility? Do you want/need to plan a year in advance, or more last minute?
-Maui is indisputably gorgeous. Where do you live? Will you want to make frequent visits there (for example, I live in NY and, while I love Hawaii, those 12 hour trips are not something I am willing to do annually or even every other year or so).
As posted above, Maui costs and MF's are high, so buy there if you are going to use. Keep in mind that trading in for a 1 BR or studio with a good trader elsewhere is not nearly as difficult as if you want a 2 BR July or August week, or other school vacation week. So, if you have a lot of flexibility and/or don't need/want a 2BR unit and only envision going once every few years, you may be better off buying elsewhere and trading in. But, if you want to be able to reserve a 2 BR a year in advance and know you've got it secured, then certainly buy there.
As for your original question- the only difference today between resale and developer purchases is the ability to trade your unit for points, of questionable value certainly after the upcoming points devaluation. While there is some disagreement and a little uncertainty on this, I am confident that whatever changes Marriott makes down the road will include all current owners being treated equally, if simply for the fact that they would not want to antagonize a large current ownership base. Along with the current economic conditions suppressing prices and Marriott hesitant to exercise ROFR because of the tightened credit market, that's one of the reasons I feel now is a good time to buy before any changes are implemented. There is a whole discussion on whether prices will continue to fall and there are arguments on both sides of that fence.
Good luck, and feel free to ask questions.