I don't know about this, as it will add unnecessary visual clutter in my eyes. I am quite fond of having a clean look to my left panel.
Do you not use podcasts or the inbox? Track counts appear for those nodes.
I use the inbox but not podcasts. I still keep Mediamonkey around for the latter, as there are more options to handling podcasts in MM than MB. I keep around 300+ autoplaylists and the inbox track count is the only
one that's currently displayed, something I can live with. Having all of the track counts appended to all of my autoplaylists will not only add to visual clutter but also may slow down my MB setup since it has to calculate the track count for every autoplaylist. I mean, look at any autoplaylist file, there's no tracks contained in there, so MB will have to query each one to get the playcount.