Re: Compensatory picks
Good point on the 2007 trades. I just noticed the 2009 trade for a 3rd rounder as the most recent example, and then went back to 2005 to find an example involving trading a future 3rd round pick and others for a 2nd round pick.
Values are all based on the GM and will be different for every team and every situation, but I do like your proposed 5th + future 3rd for 3rd. That's closer to what I could see the Patriots taking if we offered (of course their 3rd round pick is pretty late at #93). Patriots are probably our best bet at finding a suitor interested in stockpiling future picks, though there is always the question of whether we want to help them even more.
When looking at trading away future picks though, usually it is a team with a bad record from the season before (in my 2009 example, the Seahawks had a 4-12 record season before, in your 2007 example, the Raiders had a 4-12 record season before, both finishing 5-11 in the next season). Therefore the team trading for the future pick likely believes the team will once again have a pick early in that round in the following year.
The one example of overpaying you gave is the one example I noticed of a team with a winning record trading away a future pick (Broncos were 9-7). Again makes me a little worried about the value we would get for a future pick when I think most of the league at least sees us as a lock again to win the AFC South.
Overall I think our best value for trading draft picks will come with trading down current picks, not trading away future picks. I have liked examples you have given in other threads Dutchrudder of the Texans trading out of the 1st round.