Switching out tweeters

For you speaker tweakers.  I still love my old Snell Type D speakers but, as my ears age, I might be loving the metal dome tweeters less and less.  So, I'm wondering about switching them out for some soft dome.  I am going to start some research on this subject but hoping to get some feedback from those with first-hand experience with this type of stuff.  

I know some will probably say to just buy new speakers, and I am always perusing the local used selection.  (Just picked up some pretty sweet Dali Helicon 400 and getting to know them.)  The Snells are not going anywhere and getting old so I figure some upgrading might be worth messing around with anyway.  I am pretty handy and this could be a fun distraction for me short of buying a kit.  Which I would also like to do in the future.  

Thanks for any constructive thoughts.