They make a big difference if you use amps.
Can you quantify the difference? I mean... is it wattage-dependent? Does it sound better at low/high volume? I have a 350Z with the stock bose system (amp, sub, and speakers) with the D3 installed, and I can only turn the radio down so far... I mean at volume 0, it's off (of course), but at volume 1, the radio is actually loud if everything else is quiet. Like, when I'm driving with my girlfriend sleeping on the other side of the car, she reaches up and turns the volume down from 1 to 0, thinking that it's too loud, and she just wants to turn it down... not off.
That last part was a rant... sorry. But, I just want to know if the extra $100 for the hi-volt preouts is worth it. I have the intent of installing an amp and speakers (I just have to get them to fit somewhere in a 2-seat convertable), so the hi-volt preouts may make a difference. If I was staying stock with the Bose, I'd say forget the Premier unit.