First, there has to be some conflict going on, they might want to do some tit for tat. so if for example China has some problem with Canadians considering extradition of Huaweiwei's daughter, they will definitely single out some Canadian business people of European descent (not very common in China) rather than Canadians of Chinese descent (much more common in China). There is always enough to get you for something if they really want to, like taking pictures of a mountain and surprise...it is really a PLA military installation (but not really, it could just be a place where they have a hotel or something). Remember China is a rule by law country, not a rule of law one, so you can't really count on being treated fairly unless they want to treat you fairly.

Given the recent problems, right now probably isn't the best time for Americans (especially Americans of non-Chinese descent), but it probably isn't that bad either (no obvious singular dispute that necessitates tit for tat reaction). I guess I would go right now if I could get my kid's visa situation worked out (so he can go see grandma).

You are also just as likely not to be arrested for being a foreigner when Chinese are processed for similar violations. For example, hitting a roadblock that is targeting college kids who have smoked marijuana, they will drug test all the Chinese kids on the bus and will ignore the foreigners as too much trouble.