Like you, we love Aruba. I'm not familiar with the Occidental Grand, but my general advice it's easier to buy than to sell, so make sure you are buying when/where/size that will be good now and in the future. Of course, you can always trade (either in II or RCI, depending on which system the Occidental trades in) for other locations, but esp. if you envision returning most years to Aruba buy what you'll want to use.
Depending on the resort, it can be hard to sell, and you are obligated to pay MF's until you do. Most importantly- are you looking to buy a unit resale or from the developer? Again- I'm not familiar with the system- but keep in mind that in most cases if you buy from the developer you will be able to sell at only a fraction of the price. Depending on the developer/system, you may be able to buy the identical unit with identical privileges on the resale market for a fraction of the price. Some resales have minor restrictions which may not affect your usage or be of much value to you anyway, so if you are set on the Occidental make sure you know before you buy what the resale market is.
The other thing is- are they all inclusive? Personally, with the abundance of great restaurants in Aruba, I wouldn't buy a mandatory AI.