The functionality I miss from a GUI spreadsheet is this "simple" case:

I have a spreadsheet with 186 rows and want to select a specific cell's value from rows 6 and 127 and immediately know the sum if it happens to be 2 digits. Most of the time it's from the same column but not always.

With a GUI, this is really easy. CTRL + left click each cell and get the answer in a second. Throw SHIFT into the mix if you want a range of cells.