Currently there are two mechanisms for picking the size of thumbnails: a "cruder" power-of-two list and an arbitrary-precision slider.
First question: is it possible to customize the list in the dynamic list button? The power of 2 works great for smaller sizes, but then isn't granular enough for the bigger ones
Then a second suggestion: what I'd like to have instead is a wider slider with user defined marks (e.g., 32,64,107 etc) that would combine infinite precision with predefined sets like so:
a mouse hold (grab&drag) would allow you to pick any value from the slider
a mouse click would only land on user defined marks
This way you can have a easier to use slide (since it can now be wider and take the space of 2 elements) while allowing you to use both selection modes
The slider width can be edited while in Customize mode.
You can also make buttons (or menu items, hotkeys, etc.) to go to specific sizes if the automatic list doesn't include the sizes you want. For example:
That doesn't solve the issue of "UI mental overhead" of picking either of the two elements for doing the same thing where a slider with notches would suffice. The space savings is an extra benefit
Though given the accelerators remove the need to use mouse to select the items and reset is just a space away, it's best to just turn them into menus and make them more fit like this
etc) that would combine infinite precision with predefined sets like so:
