Heat pumps - auxiliary heat, splits, etc.

We have a 10-yr.-old heat pump with electric auxiliary heat (forced hot air w/ductwork). In the cold northeast, the system seems very inefficient during the winter. I have it set so the heat pump will shut off below 30°F and switch to auxiliary heat. During the winter, we get many nights (and a good handful of days) below 30°, so other than A/C in the summer, how much benefit are we really getting with a heat pump? I'd like to get greater efficiency, but I'm not keen on spending $20K for a shiny new heat pump, so I'm wondering if it'd be better to upgrade my auxiliary heat system to propane (we're not near a natural gas line). 

I know mini-splits are also popular, but aren't they basically powered by a compressor similar to a heat pump? Would I be doing any better with those? Where is my money best spent if I want to improve my home heating system?