Yeah, I'm fine with raising it as well. I don't think the insanely high taxes should be in full effect at $1 million, but maybe you start losing your tax deductions starting at $1 million. Or even $5 million. Then it increases to $5 or $10 million until it's in full effect.
And I think your primary residence should probably be exempt up to 250% of average or something like that.
*Edit* And frankly, if you're renting the property out at market value it should only be taxed as it is now. As, that's a benefit to society. You should be charged an extra 1% capital gains tax on every dollar that exceeds 2% of the home's market value.
But if it's just sitting empty for more than a few months you should be taxed 25% on the home's property value unless vacancy rates are over 10% and homeless rates are under 1 per 10,000 residents (you should be able to avoid this tax by listing the home for use with the local government as section 8, who will have to pay you market value).
Same for vacant land within city limits.
It should be a much better investment to allow homeless to live in the property than to let it sit empty.