Thats the theory, a richlist only shows the wallets of people that are stacking in one address. Big investors spread their coins over several small wallets or move them around so it becomes very hard to pinpoint who owns what. If a richlist shows you 90% of the coins in 10 wallets you know there are 10 big holders. If the richlist shows you 90% in 1000 .1 to 1 mil wallets you know nothing about the distribution. It´s a nice toy but nothing more than that.

Yes, there might be a few traders using multiple wallets, although most of them do not want the hassle of multiple wallets. A few big traders with multiple wallets are no reason to disregard the benefits of a richlist. A richlist is not providing rocksolid data for analysis and conclusion, but it is a valuable source of information concerning the proceedings of the coin.
It gives you the number of wallets in use, you can keep track if the number of wallets grows in time and you can keep track of the approx. number of big players involved.
On second hand it is a nice toy to look up your own position, like you say.