Do performance gains on Mountain Lion justify upgrade on low spec macs?

I foolishly upgraded from Snow Leopard on my mid 2007 iMac and broke samba sharing with my media player but mostly lagged and bogged down general performance (I have 6 gig of ram.)
In light of the mountain lion performance gains (safari screams etc!) would an upgrade from lion be advisable or are most of the improvements derived from more advanced video hardware in newer Macs?
Has anyone with a 2007 or low specced 2008 iMac upgraded to be able to report experiences ?