I find this word so general in it's applicability, as to have virtually no meaning, especially when used in the realm of human relationships. Take for instance, the assertion, "oh he's a nice bloke!" - what precisely, does that mean?
If ever this word is used to describe me (a rare occasion) I feel, if not offended, then uncomfortable. And though I appreciate it's often applied when the user is too lazy (or perhaps unable) to be more specific in their description, I suspect its frequently used to state implicitly: this person is safe; this person is no threat; this person doesn't compromise my security; this person won't upstage me. He or she is, quite simply, nice.
Being a nice person puts you in big demand, but for all the wrong reasons. It's concluded, in terms of your sociability, you're about as effective as a slap with a limp biscuit.
And nice is sought after; people even marry nice, in order to preserve their ascendancy. Well, it's their prerogative, but personally, I prefer to aspire towards equality, which is often, if not always, painful, and requires effort; but then, if you're really respecting of the rights of others, and aware of your natural tendencies to trample on them, albeit subtly, you'll have no issue with this, indeed, you'll welcome it!
Go on, test yourself! In future, when you find yourself ascribing this word to someone, try to be honest with yourself, what precisely are you saying? And if you're the recipient of such an ascription, consider what I've said, do you like being considered nice? Is nice, in view of what I've said, what you want to be?