> The goal is to make the land unattractive unless you optimize the use of the land and build high density.

That's right and it should be that way. The value of the land is a function of the success of the local community - it shouldn't be captured by a private investor while workers continue to pay income taxes to service and improve that land.

But if your only objection is that elderly/disabled landowners shouldn't be pressured to pay taxes many states already have laws like that in place, eg https://www.state.nj.us/treasury/taxation/ptr/