We don't ever stop long enough to need the cabanas at the waterparks. They are a bit on the pricey side, and like other's have stated you should be able to find a spot to sit if you need. If you plan to let the kiddos do all the rides, while you lounge all day then it may be worth it to you. DH and I stay on the rides/attractions with the kids so we definitely don't need it. I think the only time we sat was for lunch. LOL.
Resorts we've stayed at over 17 trips: ASMo, ASMu, ASSp, PC, CSR, CBR, POR, POFQ, WL, AKL Jambo, AKL Kidani, Poly, BC, YC, BWV, OKW, SSR, Swan, Shades of Green, Vero Beach
Next Trip: Thanksgiving 2013. WL and POR