For most of us here photography is a hobby, and (at least for me) a bobby MUST BE FUN. I love fast primes and use them mainly for environment portraits. - But do I get better photos with those fast lenses? - I think so as they give more possibilities and they are just FUN to use.
And about head portraits - they can be very boring, and there are even more boring examples than those above (I just visited a terrible exhibition). However head portrait can be great. As example I love some photos of Hans Gedda - htttp://hansgedda.com/ - Nelson Mandela, Andy Warhol etc. But I agree, you often don´t need super lenses for those studio portraits.
And about head portraits - they can be very boring, and there are even more boring examples than those above (I just visited a terrible exhibition). However head portrait can be great. As example I love some photos of Hans Gedda - htttp://hansgedda.com/ - Nelson Mandela, Andy Warhol etc. But I agree, you often don´t need super lenses for those studio portraits.