I also have to disagree with you about some points: I don't think the change in the icons will be too disruptive (most of the toolbar icons are pretty similar, but more polished) and I don't think the reason of unifying the look of the most important free graphics applications isn't compelling enough. The current icons are perfectly OK, but a lot of people find them too cartoony/childish for a capable application like Inkscape.
Unfortunately we are only a few discussing this. I'd like to know how the community feels about this. Defaulting the Tango in SVN set would be a nice opportunity to see what's the reaction of a larger portion of the users. If the majority want the old icons back, it's only matter of reverting the change and that's it.
I have to agree here. I've really been hoping for Inkscape to switch to Tango for a long time!
Joel