The benefit of a single element eidolon team would having a bunch of attacks in that element to choose from. I don't know whether the bonus elemental % from the main is applied to it though, or the himes or weapons equipped. If so, that could really add up to significant damage, esp factoring in their quick summon rates.
But your inventory space is limited, unless you want to dedicate jewels that would be better spent on gacha draws in order to expand it. R's should still be considered expendable and temporary, but you could optimize their use while you have them.
EDIT: Have Ice and Light Disaster eidolons been implemented? After getting Fire and 2 Lightning Disasters I started farming ice and light raids, because those are the only elements I don't have SRs for. But neither of them have dropped for me.