In a word, yes!
I agree with your description of the sound of the 20, and the 30, whilst broadly sharing a similar sonic character (extremely resolving and clean) has a very different balance.
The bass sounds light on the 30 directly after the 20, but after a very short time it sounds 'correct' - just as extended, and much more authoritative than most open back hp's, but clean (undistorted) and at the proper level. The mids are much better as well to my ear, being properly balanced. Certainly I was immediately aware of the broad suck-out around 2kHz on the 20 and the 30 is much improved there. There's also an improvement higher up IMO, possibly partly due to the advantages of the open back design. FWIW the 30's do seem more like a semi-open design to me.
I wouldn't say that the 30 is an 'upgrade' to the 20, but a compliment - one being open and the other closed. However, I would say that the 30 would be the preferable headphone for anything other than situations where you need a closed back. The possible exception would be situations where you might want that extra (and incredibly good) bass, such as watching a movie.