I agree with what @tombarrettillo is saying. At the moment the perspective of the crane and coin don't line up with each other and having it facing more towards the viewer would look better too.
As for the concept, one idea that comes to mind is perhaps including a character on top of the piggy bank putting in their money (such as a parent) would help with the idea of one person contributing and the bank is helping too. I think you also need to push forward the idea of growth and scale (the crane of course helps with that) but maybe having a small child standing next to he bank looking up would help or by having other smaller piggy banks around.