Not enough justification for me to buy the 60 EFS lens IMHO. I have (at least it was cheap!!) and have used the Canon 50 macro under water as well but that is no justifcation for Canon not having brought this lens up to date.
Its tricky because the design ethos of the 60EFS and the old 50 macro is quite different. The 50 macro works well on extension tubes at reasonable magnifications whilst the 60EFS is already soft on the 25mm tube. The optical design is quite different with different characteristics. So whilst the 50 certainly should be updated, the newer design of the 60 makes it easier and faster to autofocus and it does so without the lens changing length. My guess is that the 50 macro could all too easily be discontinued without a similar replacement because it represents 'old' technology. Which will be a pity because the new design of macro lenses does not lend itself to increased magnification well with extension tubes.
Perhaps I should add that there is hope. Sony's 50/2.8 FE macro recently released is of the older style design so perhaps Canon might just do something?