Your design is really good, design-wise (and subject to personal taste). And one thing is for sure, we all are looking forward to see refresh and modernization of some sorts.
Interesting is how you realized the paradigms of the desktop (WIMP) with the design language of the Metro interface (that Microsoft originally targeted for different paradigms).
Though there are some challenges, namely SketchUp is a multi-platform software and tries to use user interaction concepts that are shared by all supported (and future supported) operating systems. Symbolic or monochrome icons work well for a small repertoire of items but how do they work with huge amounts of icons (see John's studies)?
Actually John's screenshot collection is a good point to start, what if we share mockups how we imagine SketchUp to become modern (again) and to develop in future? Maybe we have to raise the bar by creating attractive and convincing "images" to underline our list(s) of feature requests?