Hi Emanuele,
When I am teaching people HTML or wikitext, I like to let people know up front that it will require a little more brain-power than they are used to with Word and similar, but that they will have a ton more control over the final outcome if they stick to the slightly more technical method.
I just talked to one of our wiki editors who is an expert in her field, but not exactly a tech expert. She said she really liked using the wikitext, for links especially, since she didn't have to break her train of thought to make the link. She said she was more afraid of creating or changing a page which would affect the whole wiki structure than nervous about using wikitext.
I think you should stick to the basics in your introduction and as your users come to more advanced problems show them more wikitext. I don't think someone who has never written html tables could understand wikitables on their first day.
Good luck! I don't think you will have as much phobia to overcome as you think, some of them might even find it fun.
-Courtney