Then the onus is on you with your massively oversized car to park properly in a space and not block others in. Park further away or in a different space if you're going to physically block entry. I don't condone keying cars, but this entitled 'my car is big what do you want me to do about it' behaviour is typical of today's society. You chose to by a stupidly big car, you should be the one inconvenienced, not everyone else.
Apart from the fact that some people have a very good reason for needing a big car - disability, big families, work-related etc. etc. - I don't think it's as simple as all that. We have a VW Golf - an old one that's considerably smaller than the newer versions - and we find the spaces very tight too.
You might be in the happy position of having both a small car and good health allowing you the agility to get in and out with minimal trouble, but you can't just go telling everybody else in quite average-sized modern cars that it's all their own fault.
Keep the same number of spots. Make some 6 inches smaller and some six inches bigger. Mark the smaller spots for small cars. Would encourage people to buy smaller cars to have more parking options.
It's a good idea, but it would be misunderstood and abused. Aside from owners of tiny cars taking the big spaces (maybe not unreasonably) 'just because' it's nicer to have plenty of room, you would get people with average/bigger cars getting angry with them and demanding they move to a smaller space, potentially causing scraps in car parks. If there are only small spaces left, people in bigger cars would park across two spaces. Then, in paid-for car parks, you'd have demands to pay less for the smaller spaces.