The C70 is BEAUTIFUL...hah, the folding top is a work of art in itself.

I don't know much about sound...and I think the K&N filter is about as far as you can go for "cheap" upgrades. Whenever I think Volvo, I always think ECU upgrades for some reason.

Here's what I can tell you about the engine though. Being that it's a five cylinder, you may notice that it's a little rougher. It's hard to balance an odd amount of cylinders, you know? There may be some issues with cold starts, but the weather down here rarely will get cold enough for that problem. Really, I think you'd only have to worry about the electricals...but much later on, being that it's a brand new car. Volvo builds solid engines...it's the other little annoyances you'd have to worry about, as with most European cars.

Hah, I was looking at owner reviews for the S60 with the same engine, and I come across this.

Unexpectedly high fuel consuption above 200 km/h (125 mph).
I LIRLed.