There is a stickie thread just for FT members to request owner referrals (i.e. the same offer you received): Looking for Marriott Vacation Club owner referral. It might be worth perusing through that thread to see some of the various comments. Also, there is another thread on the 90-minute sales pitch you will have to go through: Marriott Vacation Club 90-minute sales presentation. It includes discussions on the merits of the different offers for sitting through the 90-minute sales pitch.

Basically, some people find these offers very enticing and others not so much. But given the size of the sticky thread, you won't be alone in purchasing one of those "special invitation" MVCI packages. Just remember, they are doing this to sell you timeshare week(s) of which purchasing directly through MVCI rather than on the secondary market probably means it will be way overpriced.