hey - caught your edits - i think speedster humps, if left open to the front, would catch air and rip off, or at least direct too much heat and noise towards the driver. note also that the tonneau cover opens forward, so that mechanism could not be used if the cover were to be extended. for cooling vents i was thinking something like this:
550 coupe
but on a panel that looked kinda like this:
boxster prototype
or a combo of these:
speed humps
if you kept the stock soft top you would not need the vents, but would have to remove the custom panel and reinstall the original panel every time you put the roof up. or, you could delete the soft top and have a small custom job sewn like this:
spyder roof
if you deleted the roof you could also delete the engine cover - i've just learned of the clear covers, or you could go without, in which case you would need the vents and to use the custom panel to isolate the passenger compartment from the engine compartment like this (note the red trim piece that joins the body panel with the bulkhead):
550 cockpit