While I find Durantium and Prometium to be more abundant than the other resources, there are way too many things requiring Durantium. Prometium is almost as bad, but not quite. And I'm not talking about optional stuff like prototype weapons and modules: factories, labs and starbase modules all require resources, and that's mostly Durantium and Prometium.
I've read about the black market, but it's not available in Crusade, and it's not right that the game balance suffers just because it doesn't seem as bad for people who have all the DLCs. Likewise, trading balance with AI is totally out of whack: AIs with supposedly warm feeling towards me ask about ten times the cost in goods and techs for the techs and stuff I'm trading for. This means trading for resources is also not a viable option.
If you're Synthetic or Silicon it's even worse, you've got the short end of the stick! Even with everything set to abundant it's hard to manufacture more than 1B population every 20 turns, per planet - and that's with no using these resources for other important stuff like factories!! As synthetic, I feel compelled to always choose abundant asteroids (Durantium) and abundant planets (Prometium). And then I need to reduce habitable planets to a minimum because otherwise I still get too little resouces compared to the number of planets. It's silly I have to deliberately limit my play options just to make the game balanced. It should be the other way round: the game should adjust the balance, especially regarding core game mechanics!
In my current game, it kind of works out, but that is mostly due to the insane bonus from Xenophobic, which really needs a nerf.
IMHO there is at least one thing that needs to change: don't require resources for spammable standard buildings - at least not before age of ascension stuff. It's not like raising your factory output from +10% to +12% would be worth special resources!