Only road is the hard one
There is no easy fix to spam or scammers.
Charging for E-mail is NOT feasible by any reasonable method. User authentication and spoofing prevention would be easier to add to IPv4 IF (big IF) we were to re-write the internet code from the groud up, and would have a better effect. We could no easier decide to start charging for web pages, or charging a penny per packet. These are just not reasonable routes, and for the most part are technically nor legally feasible.
We do have laws on the books in most countries and extradition ability to be able to prosecute these fools whereever they may try to hide. If countries are willing to hide spammers and scammers then the U.N. should set up the emargos and chop the fibre cables coming out of said country. What we are missing is an informed legilature who will create a law enforecement arm, and encourage counterpart agencies to be created in neigbor countries, who are capable of performing packet sniffing and getting quick warrants to trace who is controlling bot nets. This idea of mysterious bot nets is hooey, if ISP and government co-operate it would be easy to find the originaition of a lot internet problems.
Even if actual convictions are low, if we are actively closing and correcting compromised machines it would be an improvement, and if command machines and zombies keep falling we are making their job a lot harder at little cost to us honest folk.
Another necessary factor - a new law that would make it a misdemenor crime for neglectfully operating a broadcast system (PC) on public airwaves (the net). There are already similar laws covering other areas of broadcast (RF, radio, sound, microwaves etcl They are all legislated, if you buy a $1000 radio broadcast device and start blasting the airwaves negligently, (before you learn the basics of how not to be an ass to the rest us), well then you would get a fine, why is a PC and the net any differnet? If you aren't willing to take some basic time to educate yourself and take some reasonable steps to protect your public broadcasting device, then you should pay the fine.
Yes legislation of reasable public safety laws, and then their enforcement doesn't sound like such a sexy quick fix, but it might actually have some effect in the right direction.