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1. I think that the effort involved in this activity would be too extensive to really track users at large (this would more likely have to occur on a case-by-case basis)
2. People think 'mixers' are effective (for Bitcoin / Ethereum). They aren't. They're easily traceable. However, exchanges are often dead ends on leads (assuming that exchange doesn't give up your information).
Exchanges are so effective because they mix several dozen cryptocurrencies...internally (in their order books and systems).
If one were to send Monero somewhere (i.e., an exchange) and then cash some of it out in Ripple / Litecoin / Bitcoin Cash / XLM (some fairly unusual , but liquid cryptos), they would make the task of tracking down funds exponentially more difficult (by orders of magnitude)