He'd obviously be an excellent pickup. But the reality is, the Spurs more than likely don't have the assets to acquire him via sign-and-trade (even if the Nuggets accepted a package of McDyess's partially guaranteed contract, Blair, Anderson and either this year's 1st or a future 1st, the salaries wouldn't match, which means a third team would have to be pulled in to help facilitate the trade and what assets would the Spurs have left to entice that third team, without gutting their team?). That means they'd have to sign him outright. Financially, that's doable, if they waive McDyess instead of trading his contract and convince Duncan to opt out and sign a one year deal for $15 million, in addition to pulling off a trade such as Jefferson for Casspi.
The thing about Nene, though, besides him being injury prone and somewhat dependent on athleticism while closing in on 30 is, despite what his physique may suggest, he's not a good rebounder or shot blocker. He's actually more of a skilled, offensive type. Still, I'd prefer him over Varejao, Kaman, Biedrins, Okur, Blatche, etc.