FIVE STRING TASTE
Through the 1990s, Paul used a Wal 5 string bass in the studio and for part of his live shows from those days. Though he's back to exclusive use of the old Hofner, I think it's important to take yet another page from the McCartney bass book when it comes to 5 string bass playing. There are (at least) two ways to approach the switch from 4 to 5 string bass (where the 5th string is a low B).
One way would be to take a step back and re-approach the bass with all five strings in mind, to seek it out as a whole new instrument because in effect that's what it becomes with that approach. You've no doubt heard a number of bass players who have taken this approach, and they lean quite heavily on the low B. This can be troublesome: while we bass players tend to love low rumbling sounds, there are not many others like us out there in the world. One gets the feeling that these bass players are using their newfound low B string as a weapon to grab new power in the band sound. Interestingly enough, you generally find these sorts of bass players in the club scenes and maybe it makes sense there.
The second way is to think about your bass as the old 4-string instrument - with a fifth string available on top for effect. For one thing it makes it much easier to play without thinking so much. It's so easy, while playing, to forget that the string at the top of your neck is now a B instead of an E that it's almost survival to adopt this method both live and in the studio. Approaching 5 string bass playing in this way also causes the bass player to use the B string a bit more sparingly, and hence to much better effect.
He hits that cool low C three times actually, the first time during the first note of George's solo.
The merit of all music is, by its very nature, subjective. There are few things in music that seem to reach beyond subjectivity and nestle closer to actual fact. It would be hard, for example, to argue against the suggestion that Beethoven was a great composer. It would also be difficult to rouse up an argument that Yo-Yo Ma can't play the cello. Similarly, regardless of one's opinion of his songwriting, it's safe to say that Paul McCartney was/is an extremely talented and influential bass player. Whether on his Rickenbacker, his Wal 5 string or whatever, he remains one of the top bass players in the world. For a guy who could rest on his laurels as one of the prime innovators of rock bass playing, that is a solid testament to him as a musician.