The proof assumed that p >=11 and so the ad hoc cases from the 19th century were necessary to round it out. Moreover, the attempt to extend those ad hoc methods lead to the entire branch of algebraic number theory.

I don't recall Wiles' proof assuming that p >= 11 – can you give a reference? I can't find one quickly.

The n = 3 and 4 cases were proved by Euler and Fermat. It's prima facie evident that Euler's proof (which introduced a new number system with no historical analog) points to the existence of an entire field of math. I find this less so of Fermat's proof as he stated it, but Fermat is also famous for the obscurity of his writings.

I don't know the history around the n = 5 and n = 7 cases, and so don't know whether they were important to the development of algebraic number theory, but exploring them is a natural extension of the exploration of new kinds of number systems that Euler had initiated.

They were subsumed by Kummer's work, which I understand to have been motivated more by a desire to understand algebraic number fields and reciprocity laws than by Fermat's last theorem in particular. For this, he developed the theory of ideal numbers, which is very general.

Primes in arithmetic progressions: much of what Tao and Greenberg did here extended earlier methods in a deep systematic way that were previously somewhat ad hoc. In fact, one can see a large fraction of modern work that touches on sieves as taking essentially ad hoc sieve techniques and generalizing them.

Ben Green, not Greenberg :-).

Sure, but the ultimate significance of the work remains to be seen. Of course, tastes vary, and there's an element of subjectivity, but I think that we can agree that even if there's a case for the proof being something that people will find interesting in 50 years, that the prior in favor of it is much weaker than the prior in favor of this being the case of, e.g. the Gross-Zagier formula.