@ me how: No, you cannot enlarge the displayed portion of the dropdown list - but the list itself can cover way more than 8 entries (over 32 000 entries actually). This is the reasen, why the dropdown list shows a scroll bar, if the covered entries exceed the displayed space.
Maybe this is also of interest to you: if you select the cell containing a dropdown list you can enter the dropdown using ALT + Arrowdown. This way no mouse is needed to perform data input using the dropdown list.
Cheers! Mike