Judging from the posts I've seen, I do understand why this happened. It must make you (the moderators, admins) so tired to keep locking, splitting, deleting, ... threads of people that do not follow the guidelines. And somehow they just keep coming, even though you already put a banner on top of the site.
About the rating idea: I like it, I've seen it on other forums before and liked it there too. The only disadvantage is that people might start 'repspamming' (reputation spamming), giving eachother good ratings all the time. Making it so that you need to rate 2 other people before rating the same person again doesn't really help, they will just rate some random person and then rate the target person again. Overall, I still think it's a good idea and repspamming might be avoided if the members of this forum are of good will (and will just not do it) and moderators can also perhaps have some sort of overview of reputation changes (so they can see, if they want to, if the reason for the rating was 'valid'). This way people that are always happy to help have a high rating (if they actually helped someone) and others will have lower ratings. The good thing about this is that newcomers know if they're being helped by someone that apparently knows a lot or has a lot of experience, or someone who's either new (but might know a great deal about OSDev) or doesn't know too much about OSDev yet.
Another idea would be (like suggested before) for newcomers to only have access to a specific forum (like a newcomers forum) and access to the other forums (OS Design & Theory and announcements and such) will automatically be granted whenever they have a certain amount of posts (if they spam or are utter newbies, mods will know about it [thank you, reporting system
], otherwise, they will have access like regular members).