I guess I'll be the odd duck here and not recommend upgrading to a CK30. The skid steer quick-attach that comes on the KL130 (CK25/30/35) is a direct fit for the KL120 on your CK20S. I bought it for mine, it's reasonably priced. The KL130 loader on the CK30 is hardly stronger than the KL120, can only lift about 100 lbs. more. The CK20S should have no trouble with the auger either.
The only significant benefits from the CK30 would be the additional horsepower which could add a foot to your mower width and pull a 1 foot wider box blade. I'd say if you want to upgrade go for at least the DK35 to gain a few hundred pounds in loader capacity, or even the DK40 to get the monster loader.
-Josh