Quote "Excuse my ignorance here, but what’s the difference interior space wise between a Roadster and a Plus 4 of the 2005-2018 model cars?"
The two seaters from that era all use the same chassis and body tub. The difference in width is how the wings are cut to cover the three widths of wire wheels and one width of alloys.
So choice of two seater doesn't affect space behind the seats. However the 3.7 Roadster has a larger transmission tunnel, and although the factory added a small flare to the outer footwell panels, the footwells are marginally tighter.
Four seaters are much rarer, but obviously a lot more space behind the seats, meaning that luggage can be carried inside.
