The decision between Touring and Grand touring was an easy one for us once we looked at both. Once you add navigation to the touring (a requirement for us) there is only a $1,000 price differential and that gets you these features:
Much nicer rims that really change the overall look of the car. Leather seats vs. the leatherette stuff which, to me was very polyester-ish, kind of slippery and a little cheap looking. Full LED headlamps and tail lamps, fog lights (which also change the look of the car a bit) & adaptive headlights (a good safety enhancement). The active driving display (which also shows the navigation steps which I really like). Upgraded climate control (auto setting and not the cheap looking rotary knobs).
Now, I was able to negotiate the price down $300! Plus I got another $500 off due to an S-plan certificate I got through my employer. Then I got the dealer to include the storage accessory to organize crap in the trunk ($50). So, I got the Grand touring for roughly $200 more than the touring which is well worth all the extra features (assuming you get the premium package on the touring which give you the moonroof & Bose stereo).
I read that the 16" rims have a slightly different driving dynamic than the 18". I prefer the lower-profile tires and the difference in handling you get -- maybe a little bumpier but a better feel to me.
Regarding color, it's all subjective but this car does take to gray. I'm not a huge fan of the plastic wheel well cladding and gray masks that the best of all the colors. Gray also looks nice along with the black highlights on the 18" rims and matches the areas of red you see inside the Touring & Grand touring models.
More to come later but feel free to ask specific questions if you have them.