Please note that what makes this reasoning method so easily applicable in this case is uniformity of the abstract syntax, not of the surface syntax, which is also called concrete syntax.
Homoiconicity is a relation between the concrete and abstract syntax tree (AST) of programs and the language's built-in data structures.
No idea about you, but when I reason about programs, I spend very little time manipulating syntax. Most of the time is spent manipulating semantic objects, like predicates on the program state, whose representation is independent from even the abstract syntax of a programming language.
