What problems is Grapher solving and how is that benefiting you?
I am an academic and I use Grapher for my journal papers and reports. So, I use Grapher for publishing my research. Given time and effort, I can get superb complex graphs. This is commendable but I have major issues with Grapher 10 that I use (and probably the later versions).
Even after using Grapher 10 extensively and leaving it alone for several months, I have to re-learn all the little non-intuitive details of how it works. I do not want to take tutorials. I expect graphing to be simple and intuitive. So, I now tend to use Excel 2010.
In the past, I used to use early versions of Grapher in preference to Excel. I even used to laugh at how silly and non-intuitive Excel was compared with Grapher. But then, later versions of Grapher became worse than Excel and it keeps changing for no apparent reason (except to con us into buying a new version).
Excel, on the other hand, seems to have stayed mostly the same. I had to use Excel to modify student graphs (because they all use Excel) and when using Excel spreadsheets it is dead easy to plot Excel graphs. As I get better at Excel's fiddly presentation details, I have less reason for using Grapher 10. I can see no reason to buy Grapher 13 and would only now use Grapher 10 for special graph-intensive papers or reports.
You have allowed your software developers to ruin the main feature of early Grapher which was easy to use and had an intuitive approach. This is hugh, huge mistake. Grapher needs a much simpler interface with intuitive menus in nice drop down menus. You should abandon your own spreadsheet and just build Grapher to easily use the latest Microsoft Excel. worksheet. It is true that the early version did not allow an Excel spreadsheet and so I had to copy data from Excel to your spreadsheet and put up with its many limitations. But then Grapher was fairly intuitive and it was worth it. However, when using Grapher 10, I never considered using your spreadsheet and always use an Exel spreadsheet but it is a fiddle to set up.
So, all this is very much an opinion related to my experience. If I had a broader set of needs for graphing, my opinions might change a little but you will have to decide how much they would be likely to change. You may think that it is on the wrong track but consider this, the students I teach use Excel graphing almost exclusively and, like me, have little patience for non-intuitive formatting and even have trouble with Excel (which is why I had to learn more about Excel graphing to polish up their efforts).
I recommend setting up a software development team and have them start with Excel graphing and improve it (much fiddling still occurs in Excel graphing). Call it “GRAPHER BASIC” and watch it out-sell Grapher 13 (or whatever is the latest version) once it gets going (even though it might cost more). And don't ever make any major changes and don't offer new versions, upgrade it for free.
PS. I am away from my main computer (don't like data in the cloud) and don't have a current graph to show in the screenshot below. However, I did use Grapher 10 in the following paper Medley JB (2016) Can physical joint simulators be used to anticipate clinical wear problems of new joint replacement implants prior to market release? IMechE, pt H, J of Eng in Med, 230, 5, 347-358 and I even mentioned Golden Software in the Acknowledgements. Review collected by and hosted on G2.com.