Please post links to screenshots and/or insights of this vector app. We must learn from others.
The real strength of Dia is that it has a good collection of templates and preset shapes which make it easier to create diagrams quickly. With tools that make it easy to manage large collections of clipart and the clones functionality already in Inkscape it should be possible to provide many of the same advantages to Inkscape users.
Dia is written in C and has support for plugins written in Python.
Dia makes use of XSLT which hopefully Inkscape could share. Dia also has support for importing various file formats and it would be excellent if there were some way to share these libraries or have a shared infrastructure for vector graphics the similar to how there is the generic gdkpixbuf for raster graphics.
Alan Horkan's Dia gallery (includes screenshots)
GNU General Public License (GPL)