I do agree with the that upz is a large wastage of bandwidth. However, since many people don't faithfully close their threads, the upz somehow serve to indicate that sale is still on.
It also allows more active users to bring their threads more forward, if they are in a hurry to sell compared to others, who may be in no hurry and just putting up the sale item, to sell if a good price can be gotten.
Next about updates, if normal users are neither allowed to edit their post, non allowed to post a reply, then how do they update? BNP reduced, closing deal in XX days, found new hairline scratch on lens, throw in free stuff with purchase etc there are just uncountable ways why updates are required.
So, if members need to update but cant, what do they do? start a new post then. What next for the admin? Restrict number of new ad a registered member can make a day? Then what will those who have more to sell do? Register multiple accounts and post to the limit of how many new ads a day. The same exact thing happened in HWZ classified, and it was rather messy, everyday 80% of the new ads are exactly same as the day before.
Thus, my conclusion? The previous system was just fine.
Make changes with a specific goal, not for the sake of change please.