Is the Nordkapp glass and is it in really good shape? Just how low is the price? If it is truly a killer price and you fit in it, yes I would say it is an upgrade. I've paddled a lot of boats and the Nordkapp is one that lives up to its reputation.
But you will have to decide if your paddling locations are more suitable to the P&H, which I assume is poly, or assuming the Valley boat is composite, are you good with it around those oyster shells?