you mean something like "Dick has added Session 1234 to his favourites!" as a wall notice? I have thought about that, too.
I think I'm going to focus on a "Your Friend X has posted another track: Session 1234"-message on friends uploads first. People might add and remove their favourites quickly, so you might be bombed with messages on that. I think its a bit difficult to do good summaries of whats happened - imagine, you revisit after 14 days... right now, messages are in order of apearance... but a message about a remix to your track should stay on top longer than a message on a thumb... ideally.
I spent quite a lot of time getting the differentiation between "Dick has left a comment" and "dick has left another comment" to work, so I know theres A LOT of things to consider when working on the wall-notices... but thats something to improve, you are right.

once I at it:
I just returned to this thread looking for guidance on where I'm at right now :) This happens only when I feel like nothings pressing, so thats a good thing.
I am monitoring the wiki results on google theese days, waiting to see some impact of the latest changes which all had to do with SearchEngineOptimizing.
Created a nice moderating tool, a site to view comments ordered by time, and unrelated to the session they where left to. It will be much easier to make sure there is no spam or bad content on wiki that way, something I'm trying to fend off...
Hopin the day where we break the 400-visits mark will come soon, not much happening there in the last few weeks.
Got 1762 public tracks by the minute, 839 members, 80 active.
Next jobs:

-Wallcomments as described above
-auto-mistake-PM for people breaking declaration rules
-Cards
-Show "Club of Donors"-Members on donate page

... feeling on top of things again, burned backup CDs (now how oldschool is that) yesterday, so I feel some safety in a digital world :)