Geology is interesting I will grant that. However if you subtract life earth is much less interesting. All the rocks you can find on earth can be found on other plants in our solar system. You can go most places on earth examine all the rocks and say for each "very similar to some other rock from elsewhere". But the life in each place will be very different.

This is not to subtract from geology which is an interesting and useful study, just to say it is unlikely we would discover anything very new if we could somehow examine every planet in the universe. However if we add in life we would expect a lot of interesting variety to study.