I like it a lot, it's very well-polished. You might be able to add a couple of animations, like when picking up a coin, or something.
My biggest suggestion would be in the balance of the upgrades and their accessibility.
For instance, in order to be able to advance in the fastest, most effective way, the dominating strategy appears to be to just hold out until you can afford the best of each category of upgrade.
I don't find that kind of grind to be very enjoyable, so when the dominating strategy is obvious and not too enjoyable, then an alternate design might be worthwhile.
Perhaps you could stage the upgrades a bit. Force the player to try out other items they may not have considered otherwise.
Just some ideas.