I have a bias towards MVP but here's what I've discovered:
MVP: this was never designed to be heavily used but to test your concept/idea. it's the minimal version/commitment to code to see if your product has legs.
Scaling: if you have nothing to scale to, there's no point in putting all the effort behind planning this out. test first, then scale.
as far as how much you'll have to code to take an mvp to something that scales? that depends on how you started. if you used a solid framework, you'll probably have the conventions and tools available to use caching systems and strong orm support so you aren't stuck writing inefficient queries.
