Will comment a little something about your suggestions:
1. General off-topic thread to just talk about games with no topic regulations. Like chat, but a little bit more official and maybe even with some role-play element, if people are gonna be interested. I can create and moderate that thread.
I think it's basically covered by having the following forums:
Indie RPG, General RPG, JRPG, General Non-RPG. There you can make a thread dependent what kind of game it is.
There is also a off topic forum with topics like "Last game you bought" and "last game you finished". Of course nothing is stopping you from creating something like a "game you are currently playing" thread.
2. Contacts exchange thread. Just simple thread, where people are gonna name their PSN, Xbox Live, Steam and Twitter accounts to find some new followers or game companions. I can do it, too.
Don't think I have seen a thread like this here. I am not particularly a fan of this, but why not?
3. Role-playing games category. I know about many role-playing forum games and they can be very interesting, if there will be correct regulation. It's working like this: moderator creates some game, writes the story, situations. Then he opens thread and starting to take people. Players are creating one character that fits the story made by moderator and if m. accepted them, they join the game. And after people are chosen, in special thread moderator creates special situations for each player and they should answer on them with some decisions or just by continuing the story.
It is very interesting. Apologies if you didn't catch something, I can explain more detailed.
I have seen these, but it's rather complicated. They might work well in a forum which has a very "narrow" type of userbase and a rather strict moderation.
RPGwatch however has a big range of types of users, and this includes trolls and a rather lose moderation. So I think any attempt there would be futile.
3. Mafia category. Mafia forum games are very interesting. What about doing them here? We all love RPGs, right?
Actually never heard of that one.
4. Clan system. Clans is a little communities of people, who make sure, that forum is alive and well breathing. They create events, support activities and etc.. It can help forum, I believe. And they are easy to create. I can help with that, too.
I am not exactly sure what their point is. Maybe you can explain further how it works and what the benefits are?
5. Reputation system. VBulletin allows to add them. That is not necessary, but it would be nice to say "Thank you" to someone just by adding points to their reputation.
Yeah. They added a "like" system recently and I think a reputation system would be cool as well.
6. Non-RPG category needs to be more organized. Why not to create sub-categories for popular genres?
This is a RPG page after all.
That said, Forums only make sense if they are actually used. A forum with none or just one active thread in it isn't worth existing. And when I take a look into the "General Non-RPG"-Forum there seem to be just the right amount of active threads. I don't think that splitting it would be beneficial.
7. Category of creativity. If someone writes novels or poetry, or if someone makes nice pictures or fan-fiction, they will be able to post them there. Can help with that, too.
I think this is best on dedicated fan pages with a fixed topic (like a game) or an page covering a kind of art (like drawing). While I don't see harm in creating a forum or thread for it, I think it might become very lonely in there.
8. Game recommendations thread. All is simple here, I think.
I think that one is covered with the "last game you finished" thread. But as mentioned before, nothing is stopping you from creating an additional thread.
9. Regulations in some of the popular threads to make them more interesting to view.
Not sure what you mean with that. If you mean stricter forum rules, I don't think that many people would be happy about them besides of being more administrative work.