Well...I agree with most of you.....but like once Frank Williams said "if a sponsor gives you money....we'll spend it all" (something like this)....F1 teams aren't like a normal company they don't really have a profit cause they try to use up the maximum money possible to develop their cars.....so you can try to cut down on something but they'll just keep on using the money in other departments......if you cut on engines....they'll use it in the aerodynamics department....if you reduce the number of team elements.....they'll start giving bonuses for those who work harder.
About the brakes.....reducing the diametre....would be an intersting idea...but I'd say reducing the number of pistons in the caliper and making teams use a maximum brake system pressure.....with a pop-off valve if they exceeded the limit.....this would really increase the braking distance......then we would se who has "the balls"
but....slicks.....reduction of the tire width....and start cutting on aerodynamics.......