]I don't agree here - after all, at some point in time you simply won't have enough large outputs anymore because all outputs keep shrinking. Thus you have to combine smaller outputs from time to time in transactions (except if you want to "throw away" too small outputs regularly), which then helps to associate all those to you.
I fail to see in what way you are disagreeing with me. That's exactly what I just said.
]Furthermore, another advantage I see in a mixing service is this: Somewhere I have to get my initial coins; and if I don't mine, then buying is what I have to do. If I buy for instance at Mt. Gox (yes, I know about localbitcoins and the like, but what if there are no sellers for cash in my area?), then at least *they* know theoretically my real identity and could connect me to everything I buy with the coins. Using a mixer can break this identification from my real identity to the bought coins.
Notice that I said that a user does not need a
external mixing service for this case. If you withdraw that output to and address you control, you can create a series of transactions from that point on that splits the output in to several new outputs in a manner indistinguishable from spending it. Mt Gox will only know that you had the coins at some point; it will will have no way to know if you still have them or which outputs you may still control as change. This is exactly the same thing that mixing accomplishes, so the only remaining problem to be solved is the case of how to combine multiple small outputs into larger outputs in a way that does not reduce your anonymity.