1. It's not a problem for the Eurofighter to use active aero at subsonic speeds to stabilize it, or for the Bugatti Veyron to a pop-up wing and spoiler at the back.
It's should be like that fully automatic using sensors for pressure, ride height, speed, proximity to other cars.
There was even an active aero production car in 90s, I don't remember if it was Nissan, Honda or whatever.
This was actually a proposal for 2011, but the teams refused this set of rules because Mosley wanted to go overboard with spec-ing.
2. Blocking will not decrease until it's banned (Indycar) or becomes fatal again.
3. Only the stuff the reduces overtaking should be removed ofcourse.
4. Simple, as power increased so did the drag on GP car via rules to keep safety levels up.
300 to 500 hp (depending on track) is enough is the wheels are partially enclosed and the overall drag is reduced to production car levels (on the straights at least) instead of being 3x to 4x higher like it is now.
So go to wingless cars.
A Lotus 88 with no wings, wheel covered partially plus a Veyron pop-up spoiler - wing.
with the spoiler wing down.
spoiler wing up.