You should have some way to adjust the sound to your vehicles interior. This is whether you're building a street battle or sq setup. How much dsp is needed is dependent entirely on your preferences, gear and power used. A few thoughts about this... When I was at slamology recently I listened to perhaps 23 cars the first day. After about four hours my ears were fried and I just wanted to go back to the hotel.
I think if we should be chasing anything its tonality. I am not against or even dislike PA setups. I ran one myself when I had a horn car. (Underdash Image dynamics/supertweeters in dash.) Many of them could do with some x-over adj. and aggressive eq'ing though. I'd happily trade stage width and depth to have something I could jam out too all day.
Listening fatigue is one of my pet peeves. When I build a system I need to be able to want to listen to it for more than 30 minutes. This is at both normal and "critical" volume. There are some great PA setups out there. But a lot are just loud. You know what I mean. We use the words brittle, hot, crunchy to explain the sound.
Again this isn't me making judgements. Just personal observation. This could be achieved by more than one component if needed. 30 bands per side graphic eq'ing. ability to do 24db
x-over slopes, and perhaps an parametric eq as well would be where I would start. T/A would just be icing on an otherwise delicious cake.