I think your best option would be to use Gnome's Gnumeric to create the charts and export them as SVG. If you have them in Excel, you can actually import them into Gnumeric and from there export as SVG.
There is also an extension for Inkscape called NiceCharts that is good for creating basic pie and bar charts. It hasn't been updated since 2012, but it seems to be working nicely.
Other options are Gnuplot (a command line - with several frontends - driven interactive data and function plotting tool has SVG output for graphs & charts) and Matplotlib (a python plotting library and can also output SVG). Finally, SVG charter is a perl script dedicated to generate SVG charts on web servers.
For diagrams, Graphviz can produce structural information as diagrams of abstract graphs and networks in SVG and other vector formats.