Hi Pete
I'm not with Laminar Research, just a fellow simmer in the UK.
From my personal point of view, X-Plane 11 is far superior to X-Plane 10 in so many ways, that it would be worth every penny to make the jump from one to the other!
Please remember though, that X-Plane 11 is very system hungry, so you will have to make sure that your PC/Laptop is capable of handling it. More information on system requirements can be found at this link :-
https://www.x-plane.com/kb/x-plane-11-system-requirements/
In addition, the two versions are very different and are also not compatible with one another, so you will have to remove the X-Plane 10 file structure completely from your computer and make a clean install of X-Plane 11 from scratch.
The best way to purchase X-Plane 11 is to digitally download it from LR's website (assuming that you have a reasonably fast internet connection?) and further information on this can be found here :-
https://www.x-plane.com/kb/digital-download-install/
If not, then purchase LR's DVD set (again assuming that your PC has a built in DVD ROM device?).
Do not be tempted to purchase from Steam or any other 3rd party, as you will experience a lot of difficulty getting technical support from them later, if needs be?
Hope this helps for now, but if you require any further clarification, please ask via this post?
Regards
Paul