We have been considering adding some sort of timeshare or timeshare points to our portfolio for random 3-5 day trips here and there throughout the year, and also allowing our kids and their SO's to use and go somewhere from time to time. Perhaps we would use it occasionally to take a full week somewhere in the Caribbean or Spain or Hawaii. We can afford purchasing something from Marriott (or resale, of course) and like the MVC resorts, so I'm just trying to find that right combination of weeks and/or points that is cost-effective, like
@Dean mentioned.
I would also recommend that you look at Vistana (formerly Starwood Vacation Ownership, now part of Marriott Vacation Club) and read some of the stickies in that forum.
Some of the Vistana resorts are what we refer to as "mandatory" which means that, due to some legacy issues, even resale weeks can use points to trade internally. Those trade would be within the Vistana network, which is a lot fewer resorts than the Marriott branded resorts, but it offers exchange opportunities to Hawaii, Orlando, St John, Bahamas (Atlantis), Mexico, Colorado, and a handful of other places.
There are unknowns about how inventory will be affected now that those weeks will soon also have the opportunity to exchange for MVC points, but even if there was an impact it would likely happen over many years.
When you mentioned "random 3-5 day trips here and there throughout the year" and "Perhaps we would use it occasionally to take a full week somewhere in the Caribbean or Spain or Hawaii" it occurred to me that a Platinum 2BR lockoff at Westin Kierland, for example, might fit your needs quite well (I own multiple units there). You'd get quite a bit of "point currency" which you can use in the manner you described (excluding Spain trades - those could happen only via II). If you don't use it in a given year you can also rent it out as full 2BR or just a 1BR portion, and it rents extremely well in the Platinum season.
You can play in the Vistana sandbox quite nicely but if you bought a Vistana week you will probably at some point get offered the opportunity to enroll it in MVC if you made an additional purchase from them. If that's something you think you might do, then a Vistana "mandatory" week in Maui may offer more bang for the buck over the long run (converts to substantially more DC points), but will cost significantly more in maintenance fees each year.
Since this is the MVC board, I'll stop being a schill for Vistana