The Sales Cloud exam is good and you do really need to know the ins and outs of the system. If you do and can think through problems with the appropriate logic then you'll be fine. There are a few true generic 'consulting' questions but most of it is still based on the platform.

I felt that having my developer org was the key to me passing this exam, especially because at the time I didn't have that much experience in the platform outside of what I had done for a single company.

The Service Cloud exam to me is all about volume of information. Read everything they recommend and you'll be fine. The breadth of the information you need to know for Service Cloud is wider, so they questions may not be as in-depth for each subject area. This compares to the Sales Cloud where (in my opinion) you need to know about less items, but you need to have a better working understanding of what is going on.