From my experience with a 3.0 non-sport:

The standard suspension is more than fine. It would be the "sport" suspension on most other carts. In real-world situations (bumpy roads), the std suspension will more than hold its own even in the unlikely event of an actual on-the-edge race. You get more exciting wheels and tires on sports models, and maybe more squeaks and rattles. Either way is fine, just don't think you need the sport.

GPS probably isn't much of a factor in resale value, but it might make it easier to sell. There are modern pop-up, "big screen" GPS units that have superior potential for sound systems, have touch screens (hugely better than the computer-in-a-museum controls of the std unit), have bluetooth capability, can accept a back-up camera without a huge investment in video modules and there are iPod solutions as well.

My X has nav and I think it is a negative, despite all the updates.

As for the gas mileage issue, there are a lot of widely varying reports. My 3.0 gets 20 overall, which is very good for an almost 2.5 ton, all-wheel drive, unaereodynamic vehicle.

Cruising along a level road at a constant reasonable speed will not show much difference because you are using the same amount of horsepower in either motor. However, if you start to accelerate that mass, feel the push in the back and hear the nifty exhaust sound then there will be a big drop in the V8's mileage.

You can cruise down a level road and play with the mileage meter and read-outs. It gets fabulous mileage, over 25, doing that, but as soon as it encounters even the slightest grade the mileage plummets way, way down. That is why you get 20 overall, even with the 3.0. The X is heavy.

A big V8, big sporty wheels and tires, sport seats and all are more than just fine. The 3.0 is an excellent option with some real advantages and is no disappointment at all. I still have wheel envy, though...