Thank you, that is interesting.
The two premises seem to play off of each other nicely.
I wonder, if instead of suffering invasions, Nubia instead was able to 'slow' the Nile at the Cataracts to have it drop sediment - essentially digging small canals (and I suppose a possible shipping canal if they had the manpower/money/time) to redirect water away from the Cataract proper, and out into the lands nearby.
Heck - I even think I know where I'd suggest to give it a try - the Third Cataract. The land nearby is (relatively) flat - and there are a couple of islands that with some effort could be irrigated if work was done.
Alternatively, if the Nubians really wanted to go a bit mental they could dig up some stone for rip-rap (I mean, these guys build pyramids of their own, they have to be able to, somehow) and dump it in the narrower points of the river to purposely slow it down, trap silt, and slowly raise the river level whilst creating farmland.
The way I see it, any project that can help the Nile be of more use to Nubia, helps shift the balance between Nubia and Egypt in Nubias favour, and against Egypts (even if only in small quantities).
Side note : The idea of Nubia essentially using stone to manipulate the flow of the Nile river, seems terrifying and amazing at the same time. If doing this can increase their carrying capacity, awesome. If it increases it enough to enable building shipping canals (far off, I know), then Nubia has become baws.