To save some space, Strange Part: Buildings Destroyed = SP: BD

Link 1: Outpost's search results for "Selling SP: BD". As you can tell, prices vary a huge amount, from 5.33 to 1.66. There's many people selling it for less than 4.66.

Link 2: A trader selling a bunch of Strange Parts; the SP: BD is 1 key + 1.33, which is 3.88 according to backpack.tf's key price.

Link 3: SP: BD sold for 4 refined.

Link 4: Someone trying to sell it 5.33; the SP has yet to be sold.

Link 5: TF2 Warehouse; current stock is 94. Price is 20,330 credits, which is 4.52.

Link 6: http://www.tf2outpost.com/trade/2988665 This person was selling one for 1.66.

Link 7: http://www.tf2outpost.com/trade/1919176 SP: BD for 1 key (2.55).

I think it's safe to say that demand is lowering, so the price is lowering as well. Yes, there are people selling for far more than 4.66, but they don't seem to be getting buyers.