I like the idea of trading, but physical shops would take up a lot of space if everyone is entitled to a plot (and as you said, are commonly grief'd). Maybe adding public market stalls in the market area, as Drowse mentioned in Mumble earlier today.
I agree personal shops would be nice, but I don't like the thought of automated shops. The interaction between people is a good portion of 'survival'.
However, the daily clutter of people selling things gets cumbersome because you have to sift through help requests and general chatter. So I would also suggest a chat mod where you can have different channels you can listen to, such as "General" "Trade" "Help". The only problem is, I don't know any mods that work like this, but that doesn't necessarily mean they aren't out there because I haven't looked.
I hope something works itself out to make these matters easier for you, OP. Good luck!
P.s. You should delete and repost this in the "Suggestions" section, or request a forum moderator to move this topic to the correct area. :3