In case anyone forgot this:
I have a client-side script that will log everyone's BL ID and Name on every server I go to, so the list is constantly updating itself and adding more records. I would give it out so that everyone could participate in building a list of names, but I think people would cheat and haxx it so it submits ID 100 to have had the name "richardface" or something. You can't trust people.
I'll put the list up later if you guys want it.
In other words, such an addon is entirely possible, and I see no reason why it'd lag anything. The game is already doing all the work that you want this addon to do. It'd just need to log it, instead of not logging it. Worst case scenario is that it can't add up the bricks laid and destroyed. In this case, simply have it record, to a text file, a mark every time a brick is laid, and every time a brick is destroyed. When you close the server/game, it could, at that time, tally up all the marks, and then record that result to the logged text file.
I'm not a programmer, in that I don't know C, or C++. But I have been using computers long enough to find it hard to believe that this script would cause serious problems on a server. If I'm mistaken, then I'll admit to being wrong. But currently, I can't think of any good reason why this addon would cause a problem.
Anyway, I just thought you'd like to know that half the work is already done for such an addon. It might not be posted (and won't be, for reasons he stated above), but it certainly exists. Mouser X over and out.