What a shitty store. Which is sad, they have a lot of good products and vendors there.
Very much a matter of points of view.
I buy on both (literally doing it right now), dropped the Daz+, not doing the premium because not worth it for me, it is basically meant to be addictive - to really benefit, as someone calculated you have to spend around 50 USD per month every month.
The G3 discount you are getting is because they are old products and probably they know they can be found on the Internet for free - nothing against G3, I still happily use characters, clothes and hairs.
At least for clothes, I even go all the way to V4, and even for characters, I have many V4 installed and converted them to G3 as step for eventually G8 so I can use all kind of stuff with them.
I even still buy stuff for G3 and V4.
At the same time, most of the stuff I get with the renderosity prime (which with the yearly, I don't recall being not more expensive than Daz+) is useful and not "clearance" assets, and although Daz improved by extending the life of the tokes, the rewards points of renderosity still win IMHO because they have no expiration date.
Does not mean renderosity is forcibly better than Daz, but it is a matter of points of view and individual experience.
You just have bad luck streak, I do not have hundred of things in my wishlist, but I put a couple in the trolley, added a new thing on discounted price, put the additional discount code, and I got the discount.
Effectively, from what I have seen, Daz did get many "new" artists, but it does not seem they ran away completely from Renderosity, the impression is more that Daz must have improved the conditions for the assets creators, so many they started having assets on both shops.