Using random WiFi in addition to Tor is strongly complimentary. Tor is very good at keeping some x% of your sessions anonymous some y% of the time against most attackers, but these numbers are not 100 even against relatively weak attackers. If you surf Tor for a year maybe the attacker deanonymizes one of your sessions. This is not extremely unrealistic, and is actually probably likely to happen to at least some of the people surfing silk road in a given year, even with a relatively weak attacker. If the dreaded day comes that the attacker deanonymizes one of your sessions while you are visiting SR, you are fucked if you are using your home connection but you are still quite likely to maintain anonymity if you are using a random WiFi hotspot and taking the proper precautions while using random WiFi. So although it is definitely not absolutely required that you only connect from random WiFi access points, it does offer a significant amount of additional protection and I would suggest that bigger vendors in particular seriously consider never connecting to SR from an access point that can be tied to them.