I'd say you're wrong about Pi. First of all, there is a distinction to be made between the idea of Pi the number (which isn't important, because it is just a number) and the significance of that number. The significance of the number lies in its relation to measuring circles, which we can reason outside of empirical observation. Given the concept of a circle, we can reason that Pi*r^2 equals the diameter, even without actually measuring a circle.

The idea that Pi might equal a different number in a different universe is interesting, but ultimately doesn't follow. If you want to argue that Pi equals 3.141... because of the nature of the universe in which we live, that's pretty murky ground philosophically, but I'll let you assert it. The problem is in the "other universes" and "pseudo-universal" parts- by nature of the fact that your perception of space and time is representative of the entire universe, including that which you don't know about but could potentially conceive of, Pi must always be 3.141..., even if it is a different universe. The measurement of Pi, assuming your "other worlds" argument, still relies on your perception in empirical practice, so it's going to be the same no matter what.