I said it because taking the ACT once will very quickly give you an idea of whether you're better at it or the SAT. I also live in an area where taking the ACT is unheard of, but I got a fee waiver, so I figured I might as well use it. I very quickly learned that while I found the ACT easier, my score ended up the same, so I didn't find it necessary to retake it.
If you take the SAT and then the ACT, there are only three options: 1) you do worse on the ACT, so there's no point wasting your time with it and you should go back to studying for your second SAT. 2) You do the same on both, so [in my opinion] you should just stick with the one you prefer (which for me is the SAT, especially because the majority of the country takes it, making scores more accurate). 3) You do better on the ACT, so there's no point wasting your time with the SAT and you should stick with studying for your second ACT.
I don't really see the point in taking either three times, seeing as statistics and studies all point to a statistically significant increase in scores between first and second sittings, but not in subsequent tests. I guess it would still be reasonable to take each test twice, but I don't think it necessary because your first scores will tell you which one you are likely to score higher on if you retake.
I also don't think it will hurt you at all to just not take the ACT. Like I said before, I only took it because it was free, but I only know of one other person at my school who took it (who also got exactly the equivalent score on it as on the SAT). In the long run, there's a good chance it won't make much of a difference.