random useless thoughts---
although you can blow applets up in some distros I would not necessarily want them as big as panel icons. but I sure understand the disparity and left-right difference visually...
...that huge difference, in your picture, is the reason I went to Plank. I left the icons alone and moved the Plank away from them on the opposite side of the screen.
Looks better.
That said...could you actually increase display somehow by a certain percentage? Like 115? Or 120? then you could shrink your panel icon size to match the new big applets. It's a weird workaround, just an idea.
I do know one forum member who could tell you a definitive yes or no or maybe, as he is expert at editing .rss and this kind of stuff like this and that's @SethStorm666
edit: certain themes bump applet size up and down but not to the extent you are looking for
