There's a thread
here discussing the advantages of updating to version 20g. (Note however that I think the latest version is now 20i, and I haven't upgraded to that and have no experience with it, but I did to 20g) -- and there were two advantages for me in doing that 1. yet another way to turn pages with epubs (the L & R arrow keys around the go button), and 2. now able to highlight and activate navigation links within texts in epubs (like table of contents links, etc, (Down arrow key). The upgrade to 20g was uneventful and smooth for me, but I had the same worry you did, if it works, don't fix it.
P.S. I just found another
thread specifically about upgrading to 20i which you should probably also take a look out. Seems at least one person wasn't happy with the latest 20i and went back to 20g. So for myself, I figure I'll just stick with my upgrade from 1.x to 20g. I have no idea how you can find the older 20g version, but maybe if you do a search of this ALP forum you can find some more info.