Thanks Scott7, I appreciate the constructive feedback, I'll make the changes to the parking site..nz is a very small market and a tough one to sell undeveloped domains in.
On your parked pages, activate the 'this domain is for sale' link. While you are unlikely to get offers on these domains, this at least makes it clear to anyone who visits that they are for sale.
You could try contacting a few potential end users for the mystery flights domain. There is an active business operating using the equivalent .com.au domain.
Other than that, I would let them drop.