I do use trains quite often, but even if paranoid, I do take precautions.  In my suitcase there will be only clothes.  All other valuables like camera, laptop, money, passport, etc stay with me at all times.  I do sleep with those under my pillow, and I am a light sleeper too.   And the suitcase under the bed, as far in as possible, and with the handle away and hard to reach.
So, so far no thefts, but being aware of the probable dangers is not being paranoid. 
Another thing I do not do is to flash money or other valuables to anyone.  I just keep a few yuan (under 100 Rmb) in my pocket, the rest is in a money belt around my waist.  And my passport will be at the money belt too, with a photocopy in my pocket to allow for a request from train attendant.

If you travel hard sleeper, then there is cause for concern and for worry. I prefer to travel soft sleeper and then I have the attendant lock the compartment if I am the only one in it -- and yes, do not separate yourself from your valuables, or they will be separated from you.  Some of the newer, top-of-the-line soft sleepers on the premium runs have closed circuit monitoring in them.

so far, I dont have anything stolen. But, I do take precautions too. I barely travel myself. I let friend watch over my belongings.