IMO tipping is only appropriate if the TASC (Train Attendant - Sleeper Car) provides service.
This is my basic philosophy. Gratuities are for services rendered (and if provided in advance, as discussed on other threads, aren't gratuities at all, but bribes). Customers who reward simply because they feel it's expected or because they want to be seen as "nice people" aren't helping the overall passenger experience. Tipping doesn't keep sleeper car or railfare prices down, and if rendered inappropriately, rewards those personnel who are essentially slackers and need to find other employment.
I never tip the AWOL SCA, seen only to collect his or her tip upon your arrival. These individuals also get reported to the Conductor and to Customer Relations when I get home. I have no tolerance for this type of behavior, but I also firmly believe in rewarding well those who truly care about their guests.
Good for you; this is probably the most annoying aspect of travel and customer service. Every food and beverage sales counter seems to have the requisite tip jar out nowadays. Yet, I never see any increase in service between those who actively deposit something in those jars (other than spare change) and myself (who believes that basic counter service is included in the price of goods). At the rate society is going, can tip jars on the sales counters of Macy's and JCPenney be far behind? (And if so, will I no longer have to chase someone down to come to a register to complete my purchase?)
As to the OP's original query, I have long gotten over the feeling of "being rude" when not providing a gratuity while in a sleeper. I have had great TASC/SCAs and have generally rewarded them appropriately. Others I've barely noticed while on my trip and haven't availed themselves to be of service---or in the other extreme, are overbearing in letting you know that they are
the attendant in the sleeper and please notice what they do for you so they can presumably be appropriately compensated at the end of your journey. In the latter two cases, I simply "forget" to slip them something when I deboard.
That said, I'm pretty self-service when it comes to the train. I can only remember pressing a call button once in my multiple years of train travel and only request ice from the TASC/SCA since I can no longer get it myself. I've never requested meals to be brought to me, and have often made my own bed when it is more convenient for me do to so myself than to wait for the attendant. I've also noticed an increasing neediness among other passengers in recent years. I remember the first time I traveled in a sleeper to not being aware of what the call button was when it went off once or twice during my overnight trip. The last couple times I've traveled at peak times, I've heard the call button go off about a dozen times. It's like some passengers think of the TASC/SCA as being their personal butler while onboard. I hope those people are giving out Andrew Jacksons at the end of their trips, but somehow, I'm betting not.