Well to be more accurate, boycotting is the practice of fighting harmful use of money by witholding money. Of course that stands to reason. If your money spent in a certain way is doing harm, you can prevent the harm your money does by not putting it on the harmful path.
I’m not sure what specifically you mean by getting people to reason better (whether you are talking about voting w/money or voting on the ballot in that context). Of course ads work. Political campaigns have started leveraging the same manipulation by ads that works to get people to buy goods and services.
What we certainly know does /not/ work is people thinking they are immune to ads. Everyone thinks that, and marketers prove them wrong over and over again. Advertising is specifically designed to exploit vulnerabilities in the human mind. You have no hope of creating an advertizing-immune population. It would be an ocean-boiling type of endeavor.
Political ads are not designed for targetting unpersuadables. Over the very long term propaganda that over and over blames undocumented people for problems starts to take a toll which could pull someone out of the unpersuadable demographic. But to a great extent they influence pursuadable voters in swing regions.
You say you would not switch to voting for Trump, and yet the sole reason Trump took power in 2016 was precisely due to advertising. Read about Cambridge Analytica and Peter Thiel. If Peter Thiel had not introduced Cambridge Analytica to the Trump campaign and bought Facebook data, Trump would not have taken power in 2016. THAT is how important advertising is. C/A master-minded indentifying the most important pursuadables, did a deep analysis of exactly what issues would be of interest to those individuals, and targeted them surreptitiously.
I strongly recommend you watch the PBS series “Hacking your Mind”. This episode in particular:
https://www.pbs.org/video/weapons-of-influence-gpuj68/