Inkscape is basically a tool more suitable to designers IMHO.
I mean, you could use it create vector images (such as logo images, vector icons, vector drawings, etc), not business diagrams.
In other words (IMHO):
If you want to build business diagrams, such as org charts, flowcharts, business processes, floor plans, etc using ready-to-use smart shapes, then Visio is great.
If you want to build shapes/designs, such as logo images, generic pictures, paintings, art works, site designs, etc then probably Visio is a wrong tool.