€5k off a €55k car is no where close to promoting a mindset change when an ICE equivalent car can be had for €30k. The current subsidies come nowhere close to making a compelling case on price alone. Even at the cheapest end of the EV scale, the Renault Zoe is €28k after the grant, the ICE Clio built on the same platform is €21k.
You're back at avoiding the manufacturing of new cars. While that would of course be best, it's just not feasible, but the extended running of an ICE car is more polluting than an EV even taking manufacturing into account. To what degree is down to the distances driven and electricity source, and it's not practical to factor that into a grant model.
Cars also only have a limited viable lifesspan after which maintenance and repairs become uneconomical. Unless you devise a way to extend that, or magic up a semi-decent public transport system, new replacement cars will continue to be required. In fact EVs may end up lasting longer due to the fewer wear parts involved.
As above, holding on to the ICE while buying an EV in those circumstances only results in an additional car on the road of the 20-something year old was never going to buy a car of their own. That's not how the world works. I certainly wouldn't just be handing over a car worth perhaps €20k to my kids if they didn't need or want a car that I could trade it in. Perhaps we move in very different circles and that's just not a lot of money to you.
No, it's a higher percentage, but as with cars, the percentage is greater at the lower end of the market than at the top. The 5k grant doesn't make a huge dent in the €135k price for the fully loaded Audi eTron. And like trying to argue that someone might need an e-Tron to commute, no one needs a €5k plus eBike to commute when the likes of the Canyon
Roadlite:ON is a super bike with 120km range for €2.5k.