Dave Thompson was a big loss in my opinion, but he is still suffering from his back trouble, so maybe it wasn't such a bad idea to let him leave, Jason Carter left because he wanted to play closer to his home.
For me Adie Cambridge never really cut the mustard, but the others you mention, Burnham, Coburn (Histon have got a good'n there) and Stringfellow were all good players for City. It's interesting that the last two I mentioned, Coburn and Stringfellow, both left after falling out with Tovey, now I'm not niave enough to think that everyone will get on with everyone else all the time but it suggests that Tovey is not the easiest to get on with and if you cross him he harbours a grudge. Not a very good charachter trait for a football manager.
As for Skelly, I don't really know why he is considered a midfielder, during his time at King's Lynn he was a fullback, although he was a rightback not a leftback.