To have a consistent user experience it would be better like you wrote. But I also agree that this needs so much effort that no one should hope to get these features.
I think the proponents of the two-button solution missed a point. It seems they prefer to have two buttons because they want to speed up doing SEARCHES. For this use case Notepad++ offers some powerful alternatives:
Keyboard shortcuts for forward (F3) and backward (SHIFT+F3) searching. With support of the “Customize Toolbar” plugin one can even have toolbar buttons for both of that.
The seemingly overlooked though very useful “Incremental Search” (CTRL+ALT+I) function where forward and backward search buttons are already present. This function even provides a separate input field for the search term (which is integrated seamlessly into the UI), case sensitive search, highlighting of matches and it displays the matches count.
The also seemingly overlooked “Find (Volatile) Next” (CTRL+ALT+F3) and “Find (Volatile) Previous” (CTRL+ALT+SHIFT+F3) functions. These functions search the next/previous word under the cursor, the quickest way to start a search because its needless to input a search term somewhere.
I guess the initial intent when introducing the two-button search mode was to reduce the number of UI-elements and to simplify the work with this dialog. But the current design of the dialog has not only totally failed this aim, the oposite is the case.
In my opinion the “Search & Replace” dialog should be used for more sophisticated search/replace tasks, that’s the reason why it has so much options. And instead of complaining about missing functions and demanding changes to a program users should investigate thoroughly the UI and the options dialog, often they will find useful treasures.