It should be a very noticeable difference. In my case as soon as I turn on sport mode and the suspension tightens up I can feel every little crease and heave in the roadway... which I cannot feel on comfort mode. You might just not have as much sensitivity to it. I've driven cars with very stiff sport suspensions for over 15 years, the difference is night and day. If you can't notice it then I'd say you wasted your $$.
** Removed - Tim330i **