Servicing depends on a few things:-
How complicated something is
What exactly it is you are servicing
How many specialist tools are needed
How much skill you have
The facilities you have
Are the parts available to you.
Personally I don't have a problem servicing the vast majority of my own gear. There are however, bits of my own gear I won't touch, for example my regulator.
Simple parts like a drysuit dump valve can be taken apart by the dumbest of people and put back together again. then there are more compliated valves like the spring loaded dump valves on a BCD (not the main dump valve, but the other ones) which someone with a bit of mechanical skill can service quite easily.
In other walks of life people service other safety critical devices, for example changeing car break cylinders (I have changes master cylinders, wheel cylinders, serviced servo's and made brake pipes), why not do the same with diving gear? After all, you are endangering other peoples lives playing with your car breaks, and with diving gear, only with yourown life.
It comes down to skill, and also wether you trust your life to what you have done.
Life support equipment (for me) is a no-no, back to the dealer it goes.
Semi-citical bits (BCD emergency dump valves etc..) I am happy to do myself.
Non safety critical bits will probably get taken apart for the hellof it to see how they work.
As to wether servicing is a rip off, that just depends on how much you value having you gear looked at by some-one that is reasonably confident and competent.
For some confident and competent people, it is not worth the money as they can do the job just as well.
A good analogy for a lot of the engineers that take their own gear apart is 'would you expect bill gates to take his diving computer back to have the battery changed, if it was possible to do it himself?'
The answer to this is that he would almost definitely have the thing apart himself to look at it as he is king geek.
Jon T