Strictly speaking, I'm confused about your question of "what limitations should WE place on counterplans." If you're looking for theory blocks that apply to specific types of counterplans, people can probably give you those. If you're looking for a generic, all-encompassing framework, you're not going to find that, because opinions vary from debater to debater and situations change from round to round.
I meant in an ethical sense. What seems reasonable and what seems unreasonable? What will you do when running a counterplan and what will you NOT do? In general, this is a subjective question, not an objective one, but I know there's an objective truth behind all of it. There will be a point when you're using an abusive strategy simply to win the round, no matter whether or not it's mean. Where do you draw the line? Where do you think the line should be drawn? Will you argue for your point?
Specific anti-CP strategy is all well and good, too, and I appreciate everyone chiming in about that (really, it helps), but I was looking at a more ethical angle.