Everyone's situation is unique. For some people it makes sense to own more than one timeshare interval; for others not. For those who need (and can afford) several timeshares, what some folks call the "portfolio" approach is recommended, which is just a fancy way of saying, "think carefully about what you're adding to your collection" and recognize that your needs may change over time. Many people who own several intervals ended up with them because their needs changed (e.g., they bought something close to Disney World when the kids were small, then bought something close to home when they decided to ski or celebrate Thanksgiving locally each year, then bought in Hawaii when they could travel without the kids, and so on). A common pattern is to own something on the "weeks" side and something on the "points" side, to cover all bases. (Not a bad idea, and one that I do myself.)
That being said, I recommend against buying multiple timeshares most of the time (for most people). Why? With savvy strategies you can leaverage one form of ownership into multiple opportunities. You simply don't have to own many intervals to obtain many holidays.
Example: You could own one inexpensive week and exchange it, then rent other holidays at timeshare resorts when you want to. This works best if you can make your final plans within 45 days of your presumed check-in date. Why? Because (with RCI at least) unclaimed inventory is released into the system without restrictions at that point (since the units might otherwise sit empty).
One person whom I advised a long time ago does it this way: She owns an inexpensive South African week (that trades well) and exchanges it for her overseas and more glamorous trips (i.e., where airfare is involved, hence the need to plan in advance). When she wants to travel in the USA to "driveable" destinations, she rents units from RCI's last-minute rental inventory, using the under-45-day rule. There's usually lots to choose from. Such rentals are often only a couple of hundred bucks -- less than the annual maintenance fee on a typical timeshare. Ownership of just one week and membership in RCI allows her to meet all her travel needs.
Footnote: Some people nowadays buy the cheapest interval they possibly can just to get into the timeshare system. They don't even bank their weeks or pay an exchange fee! They simply want to be part of the system so they can rent timeshares. Other people go even further and rent intervals on an as-needed basis from reputable service providers who specialize in that kind of thing. In fact (and the developers will never say this) you don't really need to own a timeshare at all to "be in the game."
Conclusion: Buy a resale one-week interval (or equivalent resale or leased points) and play with that for a year or two. Only buy another interval after you're a veteran owner/exchanger, and only do so if you really need to.
