My question is: is there a point in trying to litigate this? I mean, can I get some compensation from people spamming me while I didn't want to? Obviously this is not worth going through a lawyer, but if I can automate the filing of the complain, and hope to make $50 each time I get an email I didn't solicit, that'd be definitely worth the trouble.
Similarly, I often close accounts, but I'm pretty sure that no company out there actually deletes my data. Is there a way to enforce this?
The "best" course of action is to file complaints with your country's privacy regulator. I say "best" in quotes because by the looks of it nobody actually gives a shit about enforcing the GDPR and the regulation is flawed in the sense that you can't actually sue a company for violating it.
In order to file a complaint you must first get in touch with the offending company, raise your concerns, and if they don't give you a satisfactory response only then can you actually raise a formal complaint with the regulator. Of course, the problem here is that even if they stop spamming you it doesn't guarantee they've actually stopped spamming everyone else, and you can't tell unless you take time to manually create new accounts to prove whether they're still in violation.
Unfortunately there isn't really a way to get money out of them for their violations. Best way is to name & shame, refuse to do business with them and/or hit them where it hurts by redirecting any further spam/marketing to someone high up in the company to annoy them directly and waste their precious time.