One of the things i’ve noticed when doing some testing for some potential challenges is that techpool actually makes tires worse in beam. the difference in 0 techpool and +15 is about 1.5 seconds in favour of the 0 techpool ones, strangely enough. This was medium tires but it’s something to keep in mind.
And regarding Aero-fixtures… As long as they are visible and not over the top (racecar type downforce, ie 200+ kgs combined front and rear downforce or more) i don’t see the reason to regulate them, rather regulate the amount of downforce created, as they can give the car a more (or less) aggressive look and feel.