Sure I could install more units but hard to justify 3K for something that wouldnt need t be used often.
I don't think it is hard to justify when people spend 10-15k installing a central system. Incrementally you are spending 3k more for that little bit of need but as a system your cost is 3k more for a system that does the job vs. one that doesn't.
Nice to have a redundant heat pump in case of failure too. If each unit (assuming you need 2) is running at 50% throttle that will be quieter, more comfortable, and perhaps more efficient than one unit running at 100%.