Let me have a try at this math...........
20000 Miles / Year Divided By 30 Miles Per Gallon = 667 Gallons Per Year
20000 Miles / Year Divided By 18 Miles Per Gallon = 1,110 Gallons Per Year
1100-667 = 433 Gallons Saved
433 Gallon * $2.30 = $995 per year
You are a fairly extreme case, putting 20000 Miles per year of city driving on and top of the scale gas prices. For you it actually probably make sense. For me it doesn't.
My miles are more more highway, were the incremental benifit drops. My gas is cheaper. And I probably can't get myself to keep a car 5 Years.
In the end it is the resale that might really be in your favor. I have this gut feeling that Hybrid's are really going to be the buzzword / sought after technology. It may make your RX440 actually hold a significanty higher resale than my RC330.
One potential problem is when Ford does the Escape, most likely really screws it up with many many problems, recalls, TSB's, like they usually do (especially with a new technology), it potentially could "drag the whole Hybred concept thru the mud". Guilt by associtation type of thing. Probably not, since Honda / Toyota are already several generations into it, with no major problems, the public probably won't draw the wrong conclusions.