The line between being polite and being nice to people is a bit like the 'chicken vs. egg' dilemma. No one quite knows where one thing ends and another one starts. Being polite is one thing. A thing that easily slips towards air kisses and superficial pretension. How many times do we say 'Hi, how are you' to people we don't recall having met before at all? The question here should be 'who are you'. Although that is easily covered up by hollow phrases such as 'I haven't seen you in ages, when was the last time I saw you', replies to which usually help to jog memories. If that fails, you can always continue the conversation regardless, because chances are, the person you're talking to doesn't remember your name either. That sort of thing happens at gigs an awful lot. You find yourself waving at strangers, just in case they recognise you from somewhere. They usually don't. But that's not the point.
On the other hand, all that being polite could easily be mistaken for pretension or just plain insanity. If you're too nice, people get suspicious of your motives for talking to them in the first place, maybe suspiciously clutching their wallets in their pockets. Also, you'll soon be the laughing stock if you're notoriously friendly, because people think you lost the plot or something. However, some people can't help being friendly. You could kick them straight in the face, they'd still smile at you. Does that make them stupid? Probably not, these people are just notorious optimists, or at least pretend to be. The latter might have to do with the fact they think that if they are nice to people, people will be nice to them in return. An eye for an eye...etc.
But when is being friendly being too friendly? The trouble starts here. Because if you're friendly to people, they might think you're either crazy (the world is a place of miserable, grumpy gits, after all) or after their money (or, alternatively, that you're trying to get into their pants). And if you're not overly friendly and don't reassure everyone just what a great time you're having talking to them, you could easily be mistaken for the impersonated arrogance. And no one wants to be considered an arrogant asshole (I would hope, anyway!).
Maybe it's best to just not talk to people in the first place. But then, that'd just be plain rude. So, whatever you do, you're stuck in conversational hell, anyway. Great.