I have a great deal of IK stuff purchased over the years - to be honest though, much of it is getting old and I have not upgraded - partly because it still does what I want (such as my stand alone Ameg Bass package) but also the whole purchase routine / custom shop process is a pain.
My version of Tracks is V1 I think, but I don't use this at all now. There was NEVER a proper upgrade price that I was aware of - I spent a lot of money on this when it first came out but unlike other manufacturers I never saw or was made aware of a proper upgrade offer / path.
Amplitube is V3 I think and use it occasionally. I don't want to upgrade that as it involves the Custom Shop and I don't want my version to stop working!
I did upgrade to Sample Tank 2 and that was mainly to allow all the other stuff like SampleMoog to work - Sample Tank 2 itself is all a bit meh I think; I have not really found a use for it.
One of the main reasons I have let IK stuff "wither on the vine" is the convoluted purchasing process, so IK, here is another person who does not particularly like your current purchasing model, such as the custom shop downloading all your stuff (as described above) I hate that with UAD but their stuff is essential to me, so I tolerate it.
This does not mean I would never purchase another IK product, but it would have to be pretty special for me to bother.
Nigel