I'll reiterate this old answer of my own here. The core points still remain solid, although I'll have to see if there are any salient recent works that cast more light on the nature of the engagement that they did have. I should also point out that moving armies by sea was not the easiest thing for a small possible return, and Rome already enjoyed having Adulis and perhaps even Rhapta in its distant orbit. There was no sense trying to run invasions up the Red Sea to Aksum or kingdoms further out that would have both ecology and numbers on their sides.