I've only recently started farming for gold on things like Powerslave (with any spare SoT), so I've been very gold poor cos I was constantly using it! I've mainly been using Ironite now to expand slots tho.
I've been thinking much the same Re: sacrifice. At least, for all the common 1-2 star characters that I have brought up to at least 4 star (tho a few are 5 star). I'm thinking of ditching all the standard ones that don't have a passive or something unique, and gaining back a ton of slots. Tho since I've pretty much equipped every one of these with talismans, I'll suddenly have a huge excess of talis which I'll have to sell off (which I might need anyway with all these damn souls).
This latest event (Angel of Mercy fragments) has been dropping common souls more than anything else in LoL. It's almost exclusively where I've gotten all mine from so far. :/