Are you just staying on Windows or do you have interest in cross-platform, including mobile?
Probably just Windows desktop for now. Seems a little difficult to do data acquisition on a mobile.
I ask that mostly because I don't really see the point of moving it just from point A to point B on the broad platform spectrum. A thorough rewrite would mean considering all possibilities.
I've always any charting directly with Excel under program control simply because users did not want charts. Rather, they wanted Excel charts that they could then work with the way they do normally.
Note that any COM Automation stuff that you might be doing with Office (Word, Excel, PowerPoint) can also be done on Mac with Mac Office (just not with COM, since that's Windows only).