Personally I'd like to see progressive real estate tax introduced. The more property you own, the higher percentage of its value you need to pay each year as a tax.
Though, personally I'm more in favor of a land value tax, I think op is on the right path. Having the tax pegged to factors like average wage / rent of an area would help landlords keep it in check, though.
This tax could also be starting not from 0% but from negative value owners of a single small property might get tax credit that could help them with their mortgage in the environment of dropping property prices. For larger families with larger single properties UBI could help.
As for land value I'd like to treat the land as just another property and include its value into the total value that the tax rate is based on. I wouldn't pay attention too much about local wages. I think that information influences property values that the tax rate should be based on.
There might be secondary effects as well. Like dropping prices of properties might make land for new developments cheaper.