I have used the copying the xml's and editing them and that works great, what i have done and am still doing on my latest game is similar to an earlier post, if you have a game that uses most of the same objects and conditions for each level, then globals is what i use, and i leave one level open and simple COPY and PASTE, and if i want the same graphic/object but to change some behaviours etc i use CLONE OBJECT TYPE.
As for the Events, i create GROUPS such as CONTROLS, COLLISIONS, CONDITIONS, DEBUG etc then you can just copy and paste them into your new Event Sheets,
Also it's worth noting i rename all Layouts and Event Sheets to match for easier and faster editing and bug finding.
That way everything is nice neat and tidy and easy to understand.