Value depends on condition I paid $400 for the last '81 to '85 set I bought. $500 for a new genuine Volvo/Cibie '86+ set and $400 for a very good used set, also '86+.

Old late style units are not all that valuable and the 4 lamp systems are so common in PNPs that I doubt they are worth much.

The plug is the same, the positions of the wires on the high/low of the 4 lamp systems is different, if you are upgrading a single round system it is plug and play. '86 and up requre adapters or cutting the factory wiring.

I highly recomend adding relays to any upgrade. The factory system runs all the current through the switch, in addition to causing voltage loss due to the long runs it overheats even with stock lamps. Add wattage and you're asking for trouble.