Not to mention that Mitchell was surplus to Sydney's requirements; when you have a starting midfield of Hannebury, Kennedy, and Parker, with Papley, Heeney, Mills, Cunningham etc running through it, you don't need an accumulator.
Gibbs, on the other hand, is a pivotal member of our midfield. For us to get rid of him, regardless of his age, would risk us going the way of Melbourne, without adequate compensation.
It's perfectly fine for them to not provide for us what we'd accept for Gibbs; we'll just keep him, and he'll remember it as the club that failed to pay what he's worth.
And I reject your implied notion that Gibbs only has a few years left. He's not slowing down, he's getting better with each year he's played in his late twenties; his skills and thinking are the basis that he plays by, not athleticism or speed. He could foreseeably play for five years, from this point. What it comes down to, ultimately, is that if they refuse to pay us what he's worth, it sends two messages; one, that Adelaide will try to poach your players, but if you hold firm they go away eventually, and two, that we value Gibbs more than they do.