The plus 8 does have a Sidescreens slot behind the seats.If you don't use it there's quite a bit of space for oddments. Also a small toolbox style lockable box built into the rear shelf. The optional luggage rack has Sidescreens holders too.
There's some space behind the seats for soft bags and coats even with the roof down. We've coped quite well and no one, repeat no one has as much cr*p as my swmbo when we go away as our friends will confirm!
Early ones had the slot and locker, later ones do not: Tarka has just an upholstered shelf.
If you don't need the seat fully back there is room behind the seats for side screens, but I tend to use the rack and use the space behind the seats for coats, and other essential stuff!
Yes, agreed, the suspension box makes the rear shelf smaller, but there is stillroom for 2 soft bags on top of essentials like Euro Travel Pack, can of goo, compressor and so on. In the photo above I'd guess that the hod is sitting up because there is a load of stuff underneath.
Also because the +8 is wider than a +4 the space between seat and door is wide enough for a large shoulder bag on the passenger side.
But as you say, for serious luggage the rear rack is essential.
