What I like most about Duviri and the Circuit is actually the randomized gear. To me it's an incentive to use different things. Specially for warframes. Like, I have all of them with plenty of forma but very few I actually played enough and refined its build.
Duviri plains is a nice change of pace from the madness that warframes are, that and being pleasing to the eyes. I didn't have much incentive besides that to revisit it but now we get the 3 undercroft portals. Hope they add something else to excuse very long runs in it.
from what I know slash mods don't increase the damage of slash procs. maybe that's why