Calibre's Main UI is different from what I was used to (DOS/Unix/Windows/Linux).

No ability to reduce the Toolbar to
Text Only (or I missed a setting

).
I got over it and Customized the Bejezus out of it in preferences
Suggested UI changes happen all the time

Some start with polite discussion on: 'would this be useful', 'If we did this...'
Similar to your issue, I was having toolbar crowding problems after adding some (OK, many

) plug-in's and turned ON the then existing second toolbar, only to discover that the 'customize toolbar' (a feature that was added a while back) did not affect the split. A simple request for the ability and it was deemed 'of interest' by a developer and a revision (including some things I had not thought about

)
My point is:
Suggest ideas that:
1) Have application to a
broad range of Calibre users.
2) Support for mass production reading devices (just because you can read on it does not mean effort to support it will happen NOW)
3) Don't 'break' existing Calibre Libraries (Some early design decisions now block some good suggestions because the upgrade path would be painful to all)
Be willing to accept delay. Some developer must be willing to take on your project. On THEIR schedule.
Be willing to accept NO. Calibre is complex (even the Dev's forget parts

of the feature set). Doing
your change might block a 'in progress' project or break support for another class of user (might be platform specific).
[/rant]