I would just add the generics, if you feel it is necessary. If the Maps and Lists are all internal and still work fine, just do @SuppressWarnings and forget about it. If they are public and part of the documentation, I would change them, as it will be confusing/annoying for programmers to work with your non-generics based Map/List as opposed to what they are used to.
You could, perhaps, wrap the classes by renaming the old ones (and remove public modifier so that they are 100% internal) and then just create some new rather short generics supported classes with the previous names. The new classes could just do some simple interfacing with the old ones through type-casting and such. I think Sun might've done that with JList in JDK7... but don't quote me on that