Ugh! a mini van...
If it were me, gas would have to be $100 / gal before I'd mini-van it. The Sequoia weighs in around 6600 lbs and the Odyssey is around 4400. 2k in weight difference is pretty big. I'd do a hybrid Highlander before anything so drastic. It's not going to have those massive hybrid mpg numbers like you see on the Prius, but it's respectable for an SUV class. I think the 06' Hybrid Highlanders are quoted at around 31-33 city & 27-28 highway mpg, but I think they usually run a little less than the sticker claims. Still it should be at least up to or better than the Odyssey.