On average I would say I get 19 mpg between city and highway in my V6, for argument lets say I drive exactly 1000 miles a month. That comes out to 52.63 gallons a month. You are all saying the V8 gets 3-4 miles less on average. So we will say that the V8 gets 16, driving 1000 miles a month that is 62.5 gallons a month.
I pay about 2.67 for gas (give or take 10 cents depending on the week). Driving a V6 it would cost me 140.50 a month to drive 1000 miles. Driving a V8 it would cost me 166.87. At the end of the year that totals $1,686 for a V6 and 2002.44. A difference of $316.44. And then add up the number of years you own your 4Runner. Also I would like to note that where I live gas is substantially cheaper than other states in the US. So my figures might be lower than yours.
So I just want to point out that by no means do I think the V8 is pointless or not a fun thing to have, but if you are buying the V8 thinking the mileage difference is nothing to worry about, you might want to think that again. However I am sure that many people don't mind paying the extra 300 a year for a V8... so if you don't mind it go for it. But the way I saw it I didn't need the power of a V8, and I wanted to get higher gas mileage so that is why I went with the V6.