Ideally, it shouldn't need to be more than that. A voting system where you rank, say, five candidates from different parties could support several small parties which are biased against in most current democratic systems.
If you thought first-past-the-post was bad, wait for the new innovative top-two system to further spread, which is flat out eliminating the third party completely.
Sounds like a run-off voting system. The French use a similar system to elect their presidents, as far as I know. Is that right? Have you looked at the French experiences?
It sort of should. Otherwise, one-trick candidates who really have no idea about economics or foreign policy can win, say, a presidential election on a campaign based on, say, pro-life vs pro-choice or prohibition or their stance on one particular social program.
Germany has proportional representation. It's absolutely reasonable for parties in those systems to run on small policy platforms, especially if they're not expecting to receive a large share of the vote.
The Pirate Party, if it gets into government, will invariably be a member of a coalition with limited power to influence policy. In the aftermath of elections it may have limited bargaining power as a balance of power/kingmaker party. In both of these situations it makes sense for it to be a "one-trick candidate", using its influence to deal with the issues that it cares about, and staying more or less quiet on issues that the larger parties care more about.