Very strong game loop! I had a ton of fun discovering new pockets of gold and figuring out how best to exploit them.
I never really felt a need to use an amplifier (it may just be that I'm not entirely sure what they do), and I DEFINITELY never felt like I needed to build a wall. I could be playing it inefficiently and wrong, but to me it felt like building a wall might hinder future expansion. At one point I tried to angle the wall at 45 degrees to bounce the balls in the direction of the face, but that just bounced the balls (which were coming in at a 90 degree angle) right back to the node from which they came, leading me to achieve the desired effect with another node and not looking at the wall option again.
Overall, this is a very good prototype and I can't wait to see what more comes of it :)