Is it ok just to save wallet.dat from multiple altcoin clients and remove the client? I have the following situation: I have mined few coins from different alt crypto-currencies and I do not want to run them any more on my machine. As far as I understood from this question, I can just copy wallet.dat from each of these altcoins, encrypt them, remove the clients and this is it.

If then someone will send me some coins and after some time I would like to use them, I can just download the client, wait for synchronization, change wallet.dat with my stored wallet and continue using coins? Am I correct?
Yes, just make certain you do not make any more transactions with that wallet or you could lose coins going to a change address (an address that is used to send back extra coins. it is not the address you sent coins from).

also make certain that you remember your password and the most imperative part: shutdown your coin client before you copy the wallet

also id suggest you back up the wallet and then remove the wallet, and finally try to copy the wallet back over, if you see it load up and your coins are there you are golden. 

another way would be do dump the privkeys and encrypt a file with just those keys in it.

source: Me, I'm an altcoin pool op