There are certainly differing opinions on bioballs, but it really depends on your tank, its livestock, and what you prefer. Bioballs do work well in providing a lot of surface area for nitrifying bacteria but they should be cleaned regularly to make sure that algae, food debris, etc doesn't build up on them. I clean mine a couple of times a year and they are not very dirty when I do clean them. A key to sucsussfully using bio balls is to have and maintain a good foam prefilter in your overflow and being sure to turn off your return pump before removing that filter for regular cleaning. I have heard that bioballs are a better option for a fish only tank and/or higher bioloads.
People do put LR rubble in their sump after removing bioballs-I don't have any experience with that and I am sure someone else will chime in on that subject.
Are you having problems in maintaining water quality parameters in your tank? And, have you taken a close look at your bioballs to see if they do indeed need cleaning?