Depends on the specifics and whatnot. Who'd I have to blackmail or bribe? What's the position worth? Better hours or benefits? etc.
Like a previous boss of mine, who was an incompetent, abusive ass, and a waste of skin to boot... do I get to blackmail him? Push him out an 8th story window? Lie and get him arrested for capital treasonterrorismchildmolestation? 'Cause I'd do that just for kicks. Any resulting career advancement would be purely a fringe benefit.
I think, for me, it boils down to a risk/reward calculation and consideration of whom I have to screw over (if any one).
Because, like you observe, promoting the "best person for the job" or using meritocratic metrics for promotions and raises and such is the exception, not the rule. It's who you know and who you blow, so know and blow away! If some under-qualified cock sucker is gonna get promoted anyway, well, the only conclusions I can come to are that they want an under-qualified cock-sucker for the job, and that there's no reason it should be someone else. I can be just as under-qualified as any cock-sucker out there, so I may as well get the spot if I want it.
There's nothing inherently immoral with tailoring yourself (or your image) to get promoted - after all, if they wanted to be meritocratic, they would be, and all your ass-kissing wouldn't matter. As much as we're told (and even like to believe) that Western society is meritocratic, it's not, so don't worry about being the beneficiary of this fact, rather than just letting your boss benefit from it.