While SpS isnt the best option fo RDM, Ive been debating on a "new way to look at SpS".
Its still the worst, but a way to make it not feel like ist a waste, is to actually use manification when its up, even if you're 50/50 or 60/60.
The reasoning behind this is that you were going to use manification roughly the same time every fight, with, or w/o SpS.
So instead of looking at it as wasted mana, Ill look at it as having landed 1+ GCD attacks before I use manification.
This is probably the only way I can justify it in my head, until I get more options in gear lol.