Since we have applications that take that amount of space just in code files alone, without considering working storage, and this code works OK on devices as old as the 7290, I would say that you shouldn't worry about it too much.
What I find kills performance is not the amount of storage, but how dynamic it is. Avoiding object creation and deletion (i.e. getting the Garbage Collection running), is probably as important as the quantity of memory used. Use the Profile and Object windows in the JDE to check this out.
You should probably consider implementing a Low Memory Manager just in case your storage does cause stress on a BlackBerry. You will find a number of references to this in the documentation, and a new video about it here:
http://www.blackberry.com/DevMediaLibrary/view.do?name=LowMemoryManager
