Getting more than 5" of insulation is worth the cost even without any rebates. That alone will save you more money than anything a heat pump accomplishes, which honestly won't be much presently. Heat pumps are about getting AC and some supplemental heat right now, and being ready for a probably-not-too-distant future where fossil fuels are prohibitively expensive.

The fact that heat pumps are already cost-competitive with gas/oil is a good indicator of where things are heading, and they're heading there fast. But we're not quite there yet.