Proper Grammar

When is “proper” grammar counter-productive? As a professional writer, I do my best to be a student of language and, when not on FB, do my best to follow generally accepted grammatical rules and writing conventions. In fact, I have even noted that others’ failure to follow these rules is a bit of a pet peeve of mine. That said, I can’t help but notice that there are times when my adherence to such conventions/rules/(traditions?) seems to mostly communicate that I am stuffy, overly formal and perhaps at least a bit pretentious (ok, very pretentious). So, I’m asking you all, do you think it better to hold to tradition to protect our language and strive for clearer more consistent communication or to adopt common usage so as to not sound like a tool? And (breaking one such rule here) don’t say, “it depends on your audience.” Cop out.
For example, I was taught (though I have heard others argue that this isn’t really a rule) not to end your sentences with a preposition. But when you say, “for whom did you buy those shoes” instead of “who did you buy those shoes for” you can sound a bit like you are applying to be someone’s butler. What say you? Hold onto tradition so that we protect language from eroding into inevitable confusion or just talk like people talk even if that means the least educated and disciplined will end up being the primary creators of the way we speak? My parenting path may be influenced by your comments here.