I think actually you are all missing the point that version 3.2.2 is the Server app for Mavericks, This does not entitle you to the Server App for Yosemite as this is not the one you paid for, as you paid for Server app for MAVERICKS.
If $20 is to much stay then with Mavericks then and update to version 3.2.2.
Just because the overall functionality of the two server app are similar does not mean you get both for the price of one. That is like saying I just because I bought a 1994 Ford Pickup means I get all subsequent Ford Pickups for free as I already paid for the thing and all subsequence models have all the same functions, therefore I should get it for free, That is naturally absurd as Apple can price their own Apps however they want - and we get a lot of Apps for free, so this is really a silly thing to get upset over.
So, it seems to me that everyone that is so upset about this is because they did not understand what they were doing (yes, Apple is a bit at fault because of timing and presentation) and are not willing to admit they made a mistake.
I nearly did the same thing. I paid the $20 as I am not a developer and moved on.