By default the Notification Area Item has a preference of Max Icon Size of 22px. This is way too small for a default. This setting prevents the Notification Area icons from resizing with the rest of the icons when increasing the icon sizes in the Panel preferences anything greater then 22. I have to change the Max size everytime I install xfce. I usually set it to 64px which allows the panel settings to manage the "Notification Area" icons. To be honest I am not even sure why the Notification Icons don't just follow the Panel Icons sizes instead having their own. This is confirmed with new installs of Linux Mint 13 XFCE. LMDE xfce and Xubuntu 12.04. I Have noticed this on both 4.8 and 4.10 Thanks
Created attachment 5126 Patch to let the panel settings handle the systray icons size.
The default systray icon size goes along with the default panel setup, so it's fine for that. Distributions can change this when changing the default panel layout. Users can also change this when they alter their panel setup. Unfortunately due to the nature of the systray it's not easy to just let it "adjust automatically", at least not reliably.
Wow! I forgot all about this. I haven't used XFCE in over 6 years. I have been thinking of giving it another go. If I do, I will let you know if this issue still exists.