Not too sure about the absence of free Wi-Fi. I had free access a few months ago at the end of the C-pier, near gate C11 (actually the pier that you will be using for your evening flight to AMS (OK624 one assumes)). Not too sure whether it is there still.

But apart from free beer the lounge also offers Internet Access. Take your Ethernet cable with you, or they will give you one at the counter in exchange for your boarding pass. And as Gnopps indicates there are also free workstations.

Also - Prague itself is quite a nice city, you might want to look around for (an extra) few hours. But then - so is Amsterdam :-)

Cheers.