Another way to reduce engine power is to do what they do in F3, the things that comeout of the engine cover are air boxes, small ones, if they had normal ones F3 cars could go VERY VERY fast in a straight line.
Also you could have a limit to how much the teams are allowed to angle the rear wing. And the diffuser size (the main part the produces the most downforce), reduce that.
And i still stick by my word by saying 1 TYRE COMPANY!! I mean if it was just michelin then they (michelin) would not have to worry about making their tyres faster because of bridgestone. If F1 had 1 tyre company then there would not be rivalry trying to beat on another. And if the tyres were standard and only had 2 compounds (soft and hard) (and of course inters and wets) all the way through the season and no developing then testing time would massivley be reduced!
About 70%-80% of testing is tyre testing!!
Slower cars and less testing, therefore less money spent!