Ummm,... thanks for the replies guys. Didn't mean to start a flame war.

I was rather doubtful of my ability to distinguish an acceptable tension by comparing wheels, i fully intend to buy a tensionmeter, but that isn't this week. having said that, i remembered that i do have a new wheel, virtually identical to the wheels in question, so gave them a comparative squeeze. They definitely need tensioning in comparison to the new wheel.
The difference is marked, even to my poor sense of these things.

So, until I can lay my hands on a meter, I'll carefully tighten the wheels while making sure i don't exceed the feel of the new wheel. There's a lot of room for more tension without going overboard.