I run new-ish kernels, I have to to get security fixes unless I want to run an ancient distro kernel or backport the fixes myself: I don't as a rule run anything that hasn't come out of the stable tree, on the grounds that this has had a lot more people running it than something that's just emerged from -rc: and even so it goes wrong about a third of the time when jumping to a new major kernel release and I have to scramble back down and submit a bug report, so if I could I would upgrade less often. (And sometimes it goes wrong on non-major upgrades within a single stable series, e.g. the ext4 corruption flap, though even that was actually introduced over a major version hop and I was just lucky not to get bitten for a few major releases. I have been bitten by typos and other bugs within stable series repeatedly, too.)
Upgrading the kernel brings not only security fixes -- so I have no choice but to upgrade -- but brings other advantages with it; right now, I'm seeing substantial increases in performance of my desktop's graphics card on every kernel release due to improvements in the Radeon KMS code. Changes to init bring what advantages? init does everything I need of it. Indeed, as I said, it could be argued that it does too much.
(For that matter, even if I had run a distro kernel until recently, I'd have been forced to stop, because e.g. Debian is still on 3.2.x and most distros are even older, and those kernels are too old to support said graphics card so I'd have lost X support, which I value rather a lot.)