X is finite because it is a direct distance.
However, because of the way that it circles, it never actually reaches either point (going from either direction), and thusly its an infinite "string" still.
Not necessarily, one can have different "amounts" of infinites. A totally different thought problem might help illustrate what I mean (I'm sure there is a real term for this that would explain it better, but I don't know it): imagine there in an infinite amount of space. Now imagine that there is an infinite amount of matter in that space. The space could be totally packed with matter, so that the two are equal, even though they are both infinite. Or there could be a foot cubed of matter for every two feet cubed of space, so that while there is still an infinite amount of matter, it is half as much as the amount of space, which is also infinite.
While the displacement X may be significantly less than the directed distance between the two end points, it could still be a lesser infinite and therefore still presents the original problem that the spiral model attempts to solve.
Or at least, I think so. It does become hard to keep one's framework straight when talking of such extra-dimensional concepts.