Like any software, there are learning curves. I have TC Pro 11.2, and I just got Pro 17. Between the two, the interface is pretty much the same (CADCOURSE Interface), but there are lots of new tools. I only have the CAM plug in for 11.2, so anything that I want to port over using the CAM I do in 11.2 rather than 17. I find I can be more efficient using the Newfangled wizards for most simple stuff.
I also have DesignCad and that's the Cad system I started with. I find I can get stuff done quicker in DesignCad since I've used it more. I guess if I used TurboCad more I'd get quicker. But for hobby stuff, I don't really get much seat time doing Cad drawings.
If you do upgrade, invest in the Cadcourse CDs (not connected to Cadcourse) It will make the learning curve shorter, and you can always pop the CD in to review. There are a couple other good Turbocad tutorials out there too. It all depends on how much time you want to spend.
For upgrading, V11.2 is about the most stable. You can usually find older versions on Ebay for much less $$$. Get the Pro version as there is much more capability. If you get V15 or 16, you will most likely want the mechanical pac, and if you spring for V17, you will want the Pro Platinum for the mechanical functionality.
If you are a student ot teacher (or your kids are in school), they have a good educational discount