Realistically, what's the threat to me if I don't patch Win10? I know in theory if there's some big vulnerability discovered my system would be in danger of getting pwned, but realistically what are the chances of that happening? And if it does, how likely am I to even be affected by it if I'm not doing anything crazy, I don't even do much banking on my PC other than the online shopping.

I think the more realistic danger is that software eventually stops supporting Win10, but I'm still playing XP and Vista games here, so even that seems far fetched.

Your computer could also be used as part of a botnet or to commit crimes from. Not all malware/viruses are used to directly steal from the target.

I think it's more likely you become a danger for others. A safe space for malware

Yeah it's just a matter of how you evaluate the threat model, I might get hit by a wormable zero day, but I also think even in that case there's a good chance I see people flipping out on HN before I actually get hit and run the update manually. I think the odds of a vuln that materially effects my LAN are low, and actually I could lose my whole computer right now and I think I would still be vastly up on time saved over the past 10 or so years that I've been strongly anti-update.

Also worth pointing out that disabling most kind of updates reduces your threat surface quite a lot. If your system isn't pulling updates there's a much lower chance of malicious code getting in that way.

Denial of Service is an attack, is it not?