Is there a website where I can view the wealth distribution of BTC and different altcoins?
I know such data are only estimates (address != holder, exchange wallets, etc.), but would still like to get a feeling of how different coins are distributed among its holders.
I think you forgot that one of the purposes of Bitcoin is privacy, so how do you expect to be having such an information? You can't have such information, but you can see transactions that are made on the Blockchain. If you have an address and follow it up Blockchain you will see all the money that is going in and out from that and maybe make an estimate of how that will be in that address.
But, if it's for you to get information on who owns the richest wallet and how much they have,then you're wasting your time because you're not going to get such an information, it doesn't work like that.
Even for other cryptocurrencies, there is nothing like that, they are all about privacy.