I seem to remember more passing, or at least attempts to pass from when I was younger. That would be in the Senna/Prost/Mansell era - maybe that is just the old 'rose-coloured spectacle' effect though. I seem to remember that with the turbos they could turn them up or down if needed to try and pass - but then they had to pay the price with increased chance of blow ups etc.
If it were me I'd take off the flappy wing and KERS and give them all a nitrous tank of pre-determined size.
I really dislike all the manipulations, especially DRS, that just seems so fake and takes away the driver's ability to decided where to pass (and completely removes the chance to defend).