A really good later McCartney album is Driving Rain. I probably wouldn't have given it a chance, but I got to see him at MSG during that tour, and liked what I heard. The CD didn't leave the car for literally months afterwards.
I think his great strength is as a melodicist, not as a lyricist. Not hard to understand, though: he was always a family man and pretty content, so wouldn't write vindictive or angry songs. I think a lot of songwriters create sorrows in their personal lives so they'd have material to write about.
I think the Concord deal is easy to understand: they're one of the few labels interested in older pop performers (see their recent James Taylor releases). Also, McCartney the solo artist is facing the same sales doldrums as others of his timeframe: as today's WSJ put it, "Sir Paul's albums have sold more than 9.4 million albums in the U.S. since 1991, when SoundScan began tracking sales, plus 2.3 million digital songs. But those numbers have fallen dramatically in recent years along with the rest of the recorded-music market. Sir Paul's catalog sold just 357,000 total albums last year, and two-thirds of those sales were generated by a live album released that year by Concord, giving an anomalous bump to the catalog as a whole. He sold just 129,000 albums in 2008."
Concord is one of the few labels still seemingly committed to CD releases, and to trying to find innovative ways of marketing them; hence, their deal with Starbucks.