Sparks can fairly easily be generated again – just mandate skid blocks with maximum wear same as they do at present with the planks.
Turbo engines and probably all the electric systems were an absolute necessity – Merc and Renault would likely have pulled out otherwise due to the complete irrelevance of previous F1 engines to what’s actually being made and sold now. Now F1 has Honda coming back (and they’ve stated that it’s because of the turbo/electric PUs) and some point to the huge sums spent on the engines (sorry, PUs)
As to mechanical grip, it’s very simplistic to looks for more of it. More grip = shorter braking distances which means less overtaking usually. And the point I made about wet races stands. I would suggest that they should look to make the wings much less effective again and open up development of venturis/ground effects as these are less affected by following another car.
Nosecones – yet another rule cockup – people said the cars would look crap/odd, nothing happened… Same as the double diffusers.