Interesting.
Well, technically, you should be at the $149 upgrade. 
In the past, I had selected the wrong upgrade price option, and I was notified at some point in the process that I did not qualify for that price.
The price differences are just brackets to acknowledge where you are upgrading from.
Again, it it exactly the same product either way.
That core X3 offer for $29 would be pretty tempting.
There are plenty of 3rd party plug-ins available, and you can always add stuff from the Cakewalk store.
I am quite pleased with X3Studio and believe it is worth the $149 you would be looking at.
Looking back, I think I have spent around $500 over the years , getting to X3 Studio.
It's a tough call. What is your inner voice telling you?
The thing to look at with the options is not so much where you are now, but where will you be in a few months or a year from now? On thing I have learned is that tools that I didn't understand or think were important, have become staples in my routine. However you slice it, It's a move forward.

cool....have fun