None of these are "problems": more the "personality" of the car and the designers.
-- And the fact that the side windows automatically move down a small amount when you open/close the doors is a unique trick.
Not true. Almost all BMWs and MINIs do this, too, for instance.
-- We've discussed the cup holders. I consider them more whimsical than useful.
Yup. Most German carmakers consider cupholders a heresy. They only added them to designs because the North American market demanded them. How? Chiefly because there were many documented cases where potential customers were walking out of dealerships once they learned VWs, Audis, and other didn't have any.
I had a 2002 MkIV GTi with cupholders that were somewhat similar to the 718s, but they popped out of the center console as a tray. They were unuse-able. Why? Any spills or condensation went directly onto the radio.
-- I'm not sure I'll ever use those small, hard-to-reach storage spots with the sliding covers behind the seats.
Hard to reach, yes, but quite useful. I, for one, am very thankful that they're there -- and those who have taken apart that area's interior trim say there is a TON of use-able space there, particularly for larger audio speakers. The issue, obviously, is engine heat ...
-- The "mouth" on my base car seems like a pointless styling detail since it isn't really a grill of any sort. Maybe it simplifies production with the 3-radiator cars.
Look closely at the front valances of many late-model cars. Most have some sort of 'fake' grill/duct/opening that's used by some other variant of the model -- and some simply have the faux panel as a styling cue and nothing more. At least in the 718's case, it's the former ...
-- I'm still deciding how to deal with the PDK paddles. For tracks days at a road course, the paddles should be fine. But for autocross, I think the +/- of the shifter (set in "manual") would be better. I never had this question on any other car.
The bigger debate among those of us who have become used to paddle shifting (it takes a while) is whether the paddles should rotate with the steering wheel or remain stationary like the stalks. Most hard-core supercars have them remain stationary as in an F1 car. Then again, an F1 car's steering wheel barely even makes 1 turn lock-to-lock. The idea with them rotating with the wheel is to encourage 3-and-9 or 2-and-10 hand positioning on the wheel. In AutoX, though, I can see why the shifter option might be tempting. My advice: figure out the paddle shifters. It will encourage more precise lines and smoother driving.