Getting back to the topic of convertibles, I think I'll be going with an automatic (due to various reasons, chief of them being able to keep the BRZ). This also expands the possibilities quite a bit.
Over the weekend I tested (all with hydraulic steering):
- 2012 Audi S5 - steering is extremely light at parking speeds, weighs up when going, but lacks feel. Overall car feels very numb. Engine and transmission (supercharged V6 and DCT) are quite nice, barking on high RPM upshifts. Seemed to be tuned for some sportiness in that department. Steering and chassis fall flat, though.
- 2008 Inifiniti G37 - steering is a little better than the Audi, but still pretty numb. Engine and transmission (VQ37 and slushbox) are super lazy, even in higher RPMs.
- 2008 BMW 335i - a winner - great steering, great engine (N54) and decent transmission (ZF 6 speed). Everything felt nice and sporty. Obviously much more isolated than the BRZ, but much better than all the other options I tried (even better feeling than the Camaro).
Next is testing a 2011 335is (with the DCT that is shared with the 2010+ 135i) to confirm the facelifted (LCI) BMWs and DCT, and if that works start seriously looking at a 2012/2013 135i to buy.
So to answer my original question - there're no manual, RWD, 4 seat convertible that can replace a Twin excepts E chassis BMWs (E88 1 series and E93 3 series). Finding them in manual is hard, and they are fairly old (last model year for both is 2013 in North America). A Camaro is a distant second if you can live with the super tall gears.