I frequently use the Gnome terminal for dumping lots of debug information of certain applications, and find myself forgetting to redirect the dumps to a file.
Selecting many lines in the terminal with the mouse is cumbersome because scrolling speed while selecting is slow.

Would it make sense to add an option Edit->Select all to the terminal to select everything in the terminal at once? 

This is also an option found in many other applications (Epiphany etc.); consistency with other applications would thus be kept.