I notice that my wife gets seriously grumpy if she doesn’t get her caffeine fix so am guessing that caffeine has long term psychological effects as well as physical.
My wife is a scientist (for food actually) and she found that if she didn't give me coffee in the morning I got grumpy. So you might have something there! I know when she is mad at me... there is no coffee and she is holding a frying pan. I think it is a lot like being a bull and she is the bull fighter. Olay! The bull always loses!
Seriously though yea it is addictive but not to the point of other stimulants. I think that we can live just fine without it, but why would you want to! Maybe I am to far gone in my caffeine addiction to give an objective point of view.
In regards to altering perception, I think that you have to look at many other factors when considering its effect on deep psychosis. In almost all of the cases that I have read or heard of in regards to suicide, where coffee could be linked, there were other issues. Did it help contribute, maybe this could be argued but that would be like suing McDonalds for contributing to the death of someone who has an eating disorder.
To sum up what I am saying with out any comic relief, caffeine is a stimulant. It has far fewer side affects on the human brain than stimulants like amphetamines and cocaine (perhaps why there is not as much data on the topic). Caffeine probably does not produce the same level of brain activity in the areas that causes people to go off the deep end. Caffeine does cause activity in the brain, and sometimes the reactions can be unpleasant, especially if you are in a deficient state of mind.
Just my opinion and I am not a doctor, although many of my friends (and wife) are in this field, but as far as me... I just say outlandish things to stir them up every chance I can get!

Gota go here she comes with the frying pan!