So the semi-antique coffee table I picked up on eBay has wobbly legs.
The table seems well-constructed but the little wooden triangular prism
leg-bracing blocks were all either cracked in two, or the glue had
separated from one face of the block or the other.

I've knocked them all off and cleaned up the residual glue from the
legs. Since I'm more of a machinist than I am a woodworker, I'm tempted
to replace them with some little pieces of lightweight aluminum angle
and some small screws. Any reason not to do that, other than purity?

If I go wood, does it matter what type of wood I use, and what type of
glue?