This, what you call "spam" has been talked about as a solution to actual spam/DDoS in the ol' Internet.

Want to send an email? Send a sat along with it. Want to show an ad? Give the viewer a sat for it. Want to hit a Web API? 402 Payment Required.

This would massively cut down on untargetted advertising due to its low clickthrough rate.

The issue is either on the UI side (need client side filters for tiny incoming tx) or there has to be a protocol extension which allows the recipient to set a minimum amount for certain activities. Or perhaps a rules-based engine (like link filtering) that allows rejecting certain transactions altogether.