In the resale market you do have to watch out whether you are buying what is referred to as a Mandatory Resort (e.g. Kierland, Maui, St. John, Harborside, some parts of Vistana Villages) or a Voluntary Resort (Cancun, among them). The adjective refers to whether the resort has mandatory Starwood Vacation Network membership or not. When you buy a Mandatory resort on the resale market you can exchange with other Starwood properties. With Voluntary resorts you cannot get SVN membership and you cannot exchange within the Starwood system. You do get a 30-50% discount buying resale so the perks of buying direct are pricey.
The Mandatory vs. Voluntary distinction doesn't matter if you buy from the developer but does affect the resale price you can get if you later decide to sell your property.
I own four Westin weeks and have been very happy with the program. You already know how much nicer it is to stay at a timeshare compared to a hotel. The Westin timeshares are very nice. I've been to Maui, Kierland and Mission Hills and all have been top notch. You won't go wrong with a Westin property.
The only decision you need to make is whether to buy direct or resale. Most everybody here will tell you to buy resale. You will save a lot of money but you do give up the hotel tie-in: no up front incentives (80K points would be worth at least $1600 to me, possibly much more if you travel abroad), no exchange for hotel points, no SPG Platinum membership (if you have enough weeks to control 559,000 Staroptions), and no perks for multiple week ownership.
On a final note, Marriott does have some pretty nice resorts too. Would you be better off just adding to your Marriott portfolio, in terms of additional perks for owning more time with them? I happen to like the Starwood program better because of the particular resorts they have, but Marriott has more locations and might have been my choice if it wasn't for the Maui properties that I own. The perks, like hotel points and the like are nice, but ultimately I own where I really want to go. For me its about the property itself with the perks just icing on the cake. Its all a luxury splurge, not a real estate investment or a savings vehicle.
