[...] if enough people were actually flooding networks with "noise" and it had a noticeable effect on the effectiveness of data analysis, there are so many interests at stake here that doing it would probably become illegal in most countries. Sweet. [...]
Yes, that is pretty much exactly what would happen - compare with DMCA laws etc. that (almost) make it illegal to fix your own stuff, lest you deprive some corporate interest or other of the income that is rightfully theirs...

Generating "smart noise" would be very hard to prevent and to make illegal. Say you are interested in Gillette shaving foam... your noisy search tool might create several decoy searches along with the real search terms, resulting in searches for "Mars Bar", "Vacations in Peru", "The relative merits of Constitutional Monarchy vs. Republic", "Gillette Shaving Foam", and "Cloning sheep Dolly". Not much traffic at all, certainly not enough to be considered denial of service or network abuse. But there is no way for Google and other predators to know which of your searches is a decoy search and which is real. So the effectiveness of their algorithms matching searchers and sellers takes a big hit, becoming much less effective.
If enough people did this, it would hurt them badly, because now the wrong ads get put in front of the intended audience, and the value of the advertising "space" drops as a result.