Now that you mention it Chriz i did notice the smaller search area as well.
When i tried to modify search items, i found it was not possible to just edit like before and had to do the extra step of right-click->Edit (typing) to do it.
I usually use aaa for alubm artist auto, so after typing it, MC then expands it to Album Artist (Auto) which then takes up all the space and the only way to change aaa is to do the right click thing. Of course this depends on how big the search expression is, but i felt if you clicked right at the end of the expression, it would automatically highlight the entire expression and all you had to do was type aaa=[another aaa] and it worked great. Did not notice this in 12.0
So an extra step in this case, would like the previous, bigger, more user-friendly search bar back.