I've learnt quite a bit, and will get round to blogging things sometime, but the main lesson is - most domains earn nothing from adverts while on sedo or other marketplaces, and a decent offer of $500+ should get you almost any domain you want.
If it's a domain that's worth much more than that (e.g. insure.com sold for $16 million), then it would have been bought long ago regardless of domain squatters. It would just have been used by some other business, so you didn't really lose out.
In general, I think those kind of domains will sell for anything around $200. If they're holding it for a sale, they'll probably want more, like $500 or more.
If they've used an anonymous registrar, you can check the domainwhois sites for a history if you really want, and contact old owners of the domains, it might still be them, but otherwise I'd say forget it - they probably don't want to sell.
My guess is that when I was blogging regularly it got enough traffic to get on some watchlist and when it became available was snapped up. But don't think it will see any traffic without me pushing it.
But I suspect you're right they don't make it easy to contact them so I don't imagine it's up for sale.
Every domain you are not going to develop & probably wont renew next year should be easily available. Parked domains should be forwarded to a hosted domain page saying "If you'd like to buy this awesome domain contact me on ..." "I'll accept [insert reasonable price ie $100]
Domains with no contact info, that are parked & have never been developed are so annoying.
Either develop them or have them forward to a decent sales page.