If the Spurs could give up their Mills fetish, Porter's bloated salary could be viewed in this light: Instead of paying Mills, Gasol's quasi-expiring and the MLE on an SF over the next 2-3 years, it would all essentially be consolidated into one much needed player.
They have enough young, inexpensive depth for it, none of them are due to get paid in the next 2 years and Porter's 3rd year is a p/o. At that point, they could try to get him to pull a Jefferson: opt out and secure more long term money at a more palatable average annual value.