I still think being able to bring the quarians and geth together is pretty fuckin good. it doesn't have that much (...alright, any) overall narrative impact, but it's an excellent moment and it didn't have to be there. same with the fate of the Krogan, I was beating myself up over having deleted the genophage research in ME2, and feeling like I've made a bad decision and am now paying the price is a -good- thing in an RPG.
admittedly, neither actually fucking mattered. but I wouldn't call it completely illusiory, because it -seemed- like it mattered. not like in DAI, where none of the side bullshit even seemed to matter and, hey, it turned out it didn't matter.