Yes, that 11 month booking window is definitely the reason to own at multiple resorts. We own at two at this point, and have certainly contemplated adding on at others. We've held off so far because money is tight this year, and because with the developer points we got on one of our contracts (bought from Disney) and the banked points that came with our other (bought resale) we have plenty of points for this year and will already be banking about a third of them, even taking three 5 day + trips this year.
We bought at AKV because we know we only want to stay there if we can get SV rooms, or Concierge. We know that getting Concierge level is a bit of a gamble even with owning points there, and that we'd have basically no chance at it if we tried to book at 7 months. We're not going to add on any more AKV points; we have enough to book at least one substantial vacation a year there, and that is enough for us.
We also have a BWV contract, bought because we love the F & W festival, and we love staying at either the BC or the BW when we attend. We knew we wanted either BCV or BWV, and were delighted to find a loaded resale contract with our use year for roughly the number of points we knew we wanted.
We will almost certainly add on again, at least once. Assuming Hawaii happens, we'll add enough points there to get a two bedroom ocean view villa once every three years. We considered a VGC add-on, but decided we just don't go to California enough to make it worth our while. We may eventually add on at BLT (or another monorail resort, if one is built by the time we're ready to buy again) so that we can get MK view. We're waiting to see just how hard it really is to get into BLT at the 7 month mark, and what our financial situation looks like in the next few years.
You'll find many people here on the boards who own at multiple resorts. I know I prefer to have all my contracts with the same use year, so that my points can be combined easily at the 7 month mark, but not everyone even does that.