Personally, I`m not a fan of signing Paul Millsap. As it was mentioned above, he wont help Spurs beat Miami. With or without him, Spurs have really thin chances against LeBron and co. I would go after guys like Gerald Henderson, Timofey Mozgov and Emeka Okafor (I do believe he has early termation and couldnt find reason for Wizard to keep him for 14mln). They should be going to be cheaper than Millsap and vets like Dunleavy, Korver etc for same roster spots and they could`ve better impact next year and future.
Or simply go all in, and try to land Al Jefferson, who is going to be the best player in this year free agency.