Thank you all for the replies.
So, to sum it up, Type-level Programming, Category Theory and consimilia represent a plus if someone is designing libraries in a “collaborative” environment, but if someone, like me, programs fairly simple applications, he can be satisfied with the contents of “Scala Programming” by Prof. Odersky et al., possibly beefed up by “Functional Programming in Scala” and “Functional Programming, Simplified”. That’s why Scala stands for scalable: it affords its user to use those aspects that best fit his needs.
As per the run-time-performance aspect, the advantage of the abstractions can be debatable, and probably wouldn’t warrant the required intellectual investments.