If you really just want to inflate the amount of money being spent, there's always room for more rent-seekers and debt collectors.
Only that, the holes are very elaborate. (Like perfumes or stupid shit like a metric crap ton of TVs nobody uses anyway because we are busy staring at a much smaller screen in our palm.)
The problem here, as with any economic ideas, is properly defining "stupid stuff". Value has to be defined on an individual basis. If someone gets more entertainment from digging holes and filling them with dirt than using their phone, then hole digging doesn't seem like such pointless endeavor. The hole digger will probably end up in better health than the phone user, too, so it's not like there endeavor is altogether pointless.
Taking options away (like cash) is a bad idea if you're optimizing society around individual autonomy. We should want as many options as possible.