I think that when you look at the majority of sites that get penalised for link activities, in the main these are for pretty obvious tactics. In most cases that I've observed, the trigger is either a large network/footprint, or obvious anchor text overuse.
I would say that even if you were to pursue the four tactics above aggressively, you're unlikely to incur much in the amount of risk with Google rankings - unless you request specific anchor text, and thus create both an obvious footprint, and (inevitably) an unnatural link profile.
Of course, there are two different ways to consider this:
Pragmatic: would the techniques be detected by Google?
Ethical: is this tactic "playing fair" according to guidelines?
It's the latter that gets the most discussion, although I always imagined it was the former that most sites would be concerned with ;)