from what i gather, theyre all very similar in that you purchase a block of weeks , which allows u access to member benefits and discoutned rates over all inclusive vs buying directly from the retailer like expedia, yahoo, etc.
the member benefits do very from plan to plan and its not so obvious what each plan consists of unless you sit down with a rep at the resort. even then, depending on how you negotiate again the prices do vary.
im on a older world vacation travel timeshare, which has a 110 annual membership fee. from what ive seen today for palace premier, the prices have risen compare to older timeshare plans on the all inclusive rates.
i think there are other plans that are similar to your traditional timeshare where you get a a set number of weeks usually 1 or 2 that you can use per year.
this is what ive gotten from talking with members so im not 100% positive.