This topic has come up in the past, and a number of people, myself included, had sold a house that had a home theater in it. It did pretty much nothing for the sale price of the house, but did help to sell the house faster.
So there is some value, but not as easy to figure out as you may think, and it will be no where near the amount you put into it.
I would just get items that you want to take with you, and build the room so that it can be used as something else if you are concerned about it.
To me, I know that I am not going to be at my current house for 20 years or anything, but if it was feasable with money and space, I would still build an awesome home theater as far as room construction, etc, even knowing that it wouldn't add much value outside of just finished square footage. Most buyers just don't know the value of the equipment, and it is a "perk" that they may want, but don't care to pay extra for. And those buyers that DO understand the value of it, most likely will have their own gear, or want something a little different anyway.
So, just buy some awesome gear, and never sell it!
