What can I say, I love my album art and Plexamp is awesome! When I click on an album cover, or even in an options menu I’d love to be able to view the album cover full screen as it’s sometimes just a little small and underwhelming. Also if there’s something small on the cover that needs to be zoomed in to read etc. It’s mainly problematic ie noticeable on the desktop version of Plexamp. I can wish can’t I?
When you’ve selected an album and you’re looking at all that tracks I feel like that would be a good place to be able to click, press / press & hold on the artwork to enlarge it or / make full screen.
Having to play the track and then having to expand the window to see the artwork, then to resize and make smaller again just feels a little counter intuitive.
Yes, click to enlarge would be great ! 
Seconded! I’ve been thinking the exact same thing, thanks for putting it down in words here 
