For a small amount of money you can create hundreds of email addresses per day so adding email verification won't change anything.
If there is real spam from newbies then admin can reduce posting limit to several posts per day instead of the 360 second limit but you need to prove that there is a heavily spam happening and it is harming the forum.
BTW
Limiting newbie participation is very harmful for a community. Newbie jail will never return: I consider the newbie-jail period to have been extremely damaging to the forum. When barriers to participation are too high, then the best people often just won't go to the trouble of joining, and the people who are willing to jump through the hoops are often people who aren't good for the community: people with nothing better to do, scammers, get-rick-quickers, etc. Having a permanent newbie jail policy would improve things a lot in the short-term, but would end up being a fatal poison to the community.
The low signal-to-noise is a real issue which seriously annoys me and is often on my mind. But as you mention, fixing it non-destructively is difficult.