Is it possible to produce such design hints (on elements padding, spacing, width, height) automatically in photoshop? Is there any plugin that can potentially do this?
You can't do that in pure Photoshop. But PNG Express extension can help you. PNG Express extension can layout your design specifications onto your design.
Looks like you can. I have not tried it yet (but I will) but specKing looks like it might fit the bill.
From their website:
Take a look at: http://wuwacorp.com/specking/