If you have 30+ projects which are skinned variations on a single game, you have to maintain 30+ code bases.
If a library event sheet or objet is improved or a bug fixed, 30+ projects have to be manually updated, and retested in case a typo was made.
Also, if you do a load of work in say R100, find a showstopping bug, and have to go back to say R95, you have to recreate your weeks of work in R95. (im now faced with probably a weeks work to revert back, and retest everything).
It would be great to be able to cut and past objets (such as sprites) keeping their instance variables and names.
It would be great to be able to cut and paste events and actions, without it rejecting it becase the object doesnt exist in the new project, even though you have created the object with the same name.
Perhaps a Library folder in the project explorer?
I alibrary item can have objects, layouts + entire event sheets (or at least some events and actions). Ideally the library item re-freshes itself from disk when you load the project, and one library item can be shared across projects.