As I stated before, I don't collect Harbour Lights for the resale or investment value.
But for those of you who do,it's real simple mathematics. You pay $100 for a lighthouse and now it is worth $200 in the market. Your investment has now increased by $100. I pay $50 for the same lighthouse and my investment has increased by $150. I am $50 ahead. If that same lighthouse falls in the market say to $75, you are now in the loss column ($25), but I am still $25 to the good.

Remember is it is not the original price of an item that determines its future value. It is supply and demand.
For example if HL made a LLOM and stopped production for whatever reason after only a thousand were produced, these would be very valuable down the road.