If you only use MC for music and video (not television) then you probably won't see much change on the surface, at least in the Windows version. However, I think there are quite a few changes under the hood with respect to stability and format support etc. For me MC20 worked very well but I upgrade each year to show my support to JRiver and to help fund the continual improvements.
Where you will see some major improvements though are in the Linux release. Even though I have a master license it didn't use MC20 on Linux because I just found it too problematic. However MC21 Linux version is so much better and I am using it much more now. This is the area where I'm hoping to see improvements with the Linux release catching up to the Windows version feature wise. I'm looking forward to the day when TheaterView appears in the Linux version.
With respect to support being non-existent on previous releases, it depends on what you mean by support. If you mean improvements and updates then it is to be expected that these will stop. No software company will continue to update previous software versions except for major security holes. However, if you mean general technical support then you will continue to get that support through these forums as you always have done.
So, basically, if you are happy with MC20 then stay with it. I know some users skip a version, so they will stay with MC20 but skip MC21 and then upgrade when MC22 comes out therefore upgrading every other year. This obviously halves the cost.
