I have two suggestions for the Find/Replace bar that I think would greatly improve the UX with minimal work:
Move the Previous/Next arrows next to the "Replace" button. I general do these two things together, replacing certain references, so I constantly find myself moving the cursor back and forth across half the window.
Change "Replace" to act as "Replace & Find" or add a "Replace & Find" button/option: Most Find & Replace bars/panels I use, when you hit Replace, it moves to the next match, I think the only one I'm aware of doesn't do this is Coda. The system behavior of OS X (at least in Apple's own apps) is for the "Replace" button to function as "Replace & Find"
I have two suggestions for the Find/Replace bar that I think would greatly improve the UX with minimal work: