Mid-80s is when these bikes first arrived. That is, there were no "early-80s" Ks.
They had some "teething troubles" to be worked out. The newer the better applies as usual.
One problem not mentioned is that they were subject to vapor locking in Summer at high altitudes.
Lots has changed since then, including available fuel.
There were some factory mods to cool the fuel tank.
One guy in our club made up a fuel cooler (radiator) for his.
Good to have knee pads on the fuel tank.
For the most part as regards early Ks, you'll find similar year Airheads worth more on the used market, although they didn't start out costing as much. Problems with new BMWs these days are trivial in comparison to what buyers of new Ks experienced.