In general, I've not had an issue with luggage, even after the 'crackdown' of a few years ago. That said, I usually handle my own luggage and don't expect any crew to do it for me (though I don't stop them if they do). I have been told by a couple of Red Caps that at least one of my bags is overweight and it's never been an admonishment, just a caution as in "Don't let any conductors touch that---they'll charge you $20!" (which would be fine with me, but I appreciated the warning). This applies to sleepers, since I've only ridden coach on the NEC (and once between stops on the CZ, where I had already checked a bag at one of the stations).
The only issue I've had is with a female Red Cap at Union Station in Chicago, who refused to put one of my bags on the cart outside the (old) Metropolitan Lounge because it was overweight (at least for her; no luggage scale was used). After that experience, I shuttle my own bags on to the train if I see she's on duty when I'm in town.
In short, it's like many things with common carriers: there are rules and rules are made to be broken, but if someone wants to enforce the rules, they will. Add to that the usual AMTK advice: the only consistency is inconsistency and YMMV.