I read these UI threads and always come away shaking my head wondering what I'm missing. I seldom see any specifics about what changes need to be made to "make it more attractive." Is it all "shading" and "rounded corners on the boxes" type issues?
I do recognize that there are some confusing aspects of the UI that could be improved with coding effort. One lies in the multiple toolbars for "device connected," "device not connected," etc., but fixing these problem areas would seem to have limited payback. The problems mostly reside in the more obscure corners of Calibre (how many users change the toolbars?), and many current users have already learned the existing setup, so we're only talking about a subset of new users who would find it easier to find and learn these more obscure features. The gain due to reduced effort for these future users has to be balanced against the effort all the existing users would require to learn a new system, plus the effort to code up the "easier" interface.
I'd support such changes for anyone who wants to go to the effort, but I'd be even happier if they put that effort into new/better features.