I like the idea of only allowing appending for the title, but maybe make the appendable part of the title unlimited for editing or else I can see the following happen if you can only append to the title with no deletes:

For Sale Stargate
For Sale Stargate $3,500
For Sale Stargate $3,500 price lowered $3,499
For Sale Stargate $3,500 price lowered $3,499 final price drop $3,000
For Sale Stargate $3,500 price lowered $3,499 final price drop $3,000, final final price drop $2,500
For Sale Stargate $3,500 price lowered $3,499 final price drop $3,000, final final price drop $2,500 now $1,500
For Sale Stargate $3,500 price lowered $3,499,final price drop $3,000, final final price drop $2,500 now $1,500 sold

So everything after the original "For Sale Stargate" is always editable even after the 24 hour lockdown. Maybe you could show all the appends in the body of the first post so people can see the title changes.

Also, maybe a dropdown box with common title editing options like adding: Resolved, Sold, Updated, Price Lowered,