The money should be spent elsewhere. The C's can't afford to be paying a 4th or 5th big man that much money, when they have several other holes to fill.
The difference is its not 7 mill incremental - its more like half that in marginal cost. Your removing the salaries (sunk costs) for Tony Allen and Scal. And beyond that - I don't think the C's are worried about single year payroll as much as long term (they would have paid Posey for three years, just not 5, they paid money to buy a draft pick, etc.)
Unless there is another (reasonable) trade possibility for Scal and Tony Allen - but I don't think you'll get much more value for those guys. I'm willing to listen. And backup Center (even if he's not first big man off the bench) is still important spot, and for all the Darko hate, he's not a bad backup. Consider the backup centers we've had, basically no one who could see the court, except PFs playing out of position.
Sorry, I wasn't clear. My issue wasn't as much about the money, but the assets we would be using to get him. We only have a limited amount of assets this summer. We have the MLE, LLE, those expiring contracts, Big Baby in a sign and trade, and vet minimum contracts to offer.
If we use the MLE to sign a big man, that leaves us with just just the trade pieces, the LLE, and vet minimum contracts in order to sign a backup PG (assuming Marbury is gone), at least one backup wing, and another back up big man (or keep Davis). At that point, our best asset will be those expiring contracts, and possibly Davis. If we have already signed a big man with the MLE, then that extra big man would be much further down the list of needs behind backup wing (HUGE need), and backup PG.
So instead of using our best remaining assets to fill the lesser need, they should be working hard to use it to fill one of the bigger needs, because it will be tough if they are stuck with trying to fill those needs with the LLE and vet minimum. We might end up in the same position we were in last year, with Pierce and Allen being forced to play way too many minutes, and House being forced to play out of position.
I will add though, that if they cannot sign Sheed, McDyess, or Zaza, this trade would be decent, if they were bringing in Darko as a primary backup big man. But you simply cannot be using assets like that on a guy who wouldn't even be in the playoff rotation if things go as planned (which Darko would not be, if the C's already had Perk, KG, and Sheed).