I am able to buy gold block upgrades without the requisite gold blocks.
It seems like one of the cost reduction upgrades is displaying the correct amount, but isn't actually reducing the cost of the upgrades. I think it's the skill mine amount (I am up to 20%.)
Also the Skill Mine idle hitters does not increase the number of idle hitters displayed, so it's hard to tell if it's working or not. It wasn't until I got to 10 idle hitters that I realized it works for every stage.