Engine vibration is killing many other effects on low and mid-range wheels (maybe even high-end too, to be honest) which is why I made the simple mod Dan has linked to. Without that vibration you can start to feel road rumble, curbs, and the various tyre scrubbing effects that were "invisible" before. Personally, I really think Reiza need to give us more customisation options for FFB because there is no "one size fits all" possible with such a subjective feature. Two sliders just don't cater well to all the different wheels and their capabilities, or to the huge range of personal preferences.
It's also worth noting that FFB varies wildly between cars right now. For example, I was testing another FFB mod yesterday. In the SuperV8 it felt completely dead, seemingly with nothing but cornering forces. Later I tried the same FFB with the same settings in the Formula V12 and... wow. The FFB blew me away, it was so alive. This is something that should be helped when the individual car multipliers are added.
Reiza have also said there are further FFB tweaks coming soon, including a minimum force setting, and that this should make the FFB good enough for the v1.0 release.