I think how much you will use a hardtop depends on where you are. I have to deal with snow for about 6-8 months a year, so I keep the hardtop on, and the significantly reduced noise makes road trips a lot less annoying. But it depend on where you are.
If you are concerned with headroom, try sitting in a Boxster with a hardtop and see for yourself. The reference to more or less than the soft top depends on whether you have a liner or not.
