
There is somethings you should think about with this hobby. Are you in it for FUN? Are you into coins for something to do? Are you thinking about this as an investment?
I say this since I many times have purposely purchased cleaned coins. Why? For one thing they can be a lot cheaper than non cleaned coins. And if your collecting coins for a hobby and for FUN, so what if they are cleaned? As long as you are happy with your coins, it should really make little difference if cleaned, conserved or just natural.
If it bothers you if a cleaned coin is to shinny, just put it on a kitchen wincow sill for a few months and the shinnyness will tone down.
As to your question, it is true that cleaned coins are not as valuable as original ones. Again, depends on what you are doing with your coins. If you are happy with those, no ones buisness but your own.