My thinking is that every little bit helps. Rebounding is really a team stat which every player contributes too. And if your SG is a good rebounder, he'll likely perform better at SF as well.
I agree, and I think individual mismatch are important, but I think the higher the division, the Higher the big guys Rebounding skills are. And it seems, the Frontcourt will tend to "Suck up" more rebounds.
A guard with 7 in Rebound is great in D.IV, if you compare with typical PF or C Rebounding skills at the same level.
But two divison Higher the same guard Rebounding is much less impressive.