I used to be an owner at that resort. Please be aware that the week being sold is NOT platinum. Harbour Point is an older resort that was not built by Marriott. The weeks are all fixed, and they are not labeled with the usual seasons (platinum, gold, silver, bronze) that most other Marriotts have. Sunset Pointe, a sister resort which was built by Marriott and shares the lobby and pools with Harbour Point, labels that week as "sport". This corresponds with a gold week at the beachfront Marriotts on Hilton Head Island. It is not platinum.
Some owners have had great success in exchanging their Harbour Point weeks through II. However, Harbour Point has a lower internal quality rating with II than most Marriotts...and it is not one of the more requested resorts within the Marriott system. If you get a great deal on a week there, then this may not matter. If you would be content to stay at Harbour Point every few years...rather than just trade it every year...that would be a major factor suggesting that this might be a good purchase for you.
If any Marriott resorts are dropped from the system within the next few years...or have their trade power diminished in a possible new Marriott internal exchange system...Harbour Point is more likely than most to be one of them. I am not saying that either of these events will occur, just that Harbour Point is more vulnerable than most other Marriotts.
Steve