No need to imagine how a soft top version will look, well the BMW teaser pic needs a bit of imagination, but you get the idea, not the Z1 or Z2 it should be but I likey
as for roof up in the roadster when it's sunny, I am guilty of this sometimes if I am tired.... i used to do many a long commute in a 3 series and never had a problem, after having the z4 a few months I noticed that after a long journey I would be more tired as if the driving took quite a bit of energy out of me and with the roof off this seemed to make things worse but no idea why...
I confirmed this again about the Z4 recently when I went to florida and hired a mustang convertible and did about 1.2k miles in it... I never got tired at all roof up or roof down and felt refreshed after every journey, it was like driving a sofa around. For some reason the Z4 commands more of your attention while driving long distance. it might be how your sat in it near the road low down or the harsh suspension or the constant wanting to put your foot down to have fun and watching for the old bill like a hawk... It certainly is a lot more fun and responsive than that mustang though despite the mustang having 300+ HP. When I got of the plane and back into the Z4 I was like ah yes this is more like it, those precise germans lol.. Maybe the newer E89 addresses the tired issue by softening things up but I imagine you cant have the best of both worlds in just 1 car.