After 3 tanks and an increase from a 38mpg average to a 43mpg average, and after making a spreadsheet based on gas prices of $3.80, I'm going to say that these two mods not only pay for themselves (over normal tires) but the tires+$80 wheel covers (if they don't fall off) are completely free over a 65k treadife. (Tires were about $100 and then there was mounting and balancing ($50 rebate, now up to $160
) Sentra SE-R's taller tires are definitely worth looking into as well, though.
There are always variables out of our control, but I am using essentially the same hypermiling techniques as when I got 38mpg, and there was definitely some stop and go freeway traffic in these 3 tanks where I could not EOC. The only very slight mod to my driving has been EOCing occasionally to stoplights when I know I won't need the engine for >30 secs, and parking lot EOC to a stop. That and stop and go traffic probably cancel each other out, or at least enough to where I feel confident that these mods are essentially free.
I also calculated the fuel savings of all my hypermiling over EPA estimates in general and I'm saving almost $10k over 200k miles at a $3.80 (conservative) gas price estimate. Essentially driving my way to a new economy car. Take that to the nonbelievers in hypermiling!