Have to agree with IIsaw there. For one, the lesser sound dampening in the SR3 would mean worse acoustics as compared to let's say, a SGTi. For better sound quality overall, you will need to at least re-install some sound deadening material for soundproofing. Number two con would be the extra weight when you plonk in a 12" sub for instance, not forgetting you amps and what naught.
But then you could argue that you could go with a Stage 2 engine upgrade :) That would solve your power-to-weight problem. The SR3 is lightweight, but the key advantage is also its chassis, which makes it a solid base platform. What you do with it after is up to you.
It all boils down to the individual. The car is yours. Bottomline is, you choose what you want your car to be. Personally I feel if I wanted a sporty, more luxury car with better acoustics and quieter in general, I would have bought a SGTi.
I wanted a no-frills, lightweight, zippy machine. It's a Lotus concept/philosophy, really. A no nonsense, lightweight car which flies. That's why I bought the SR3. I am a music lover, no doubt about that, but I feel the SR3 isn't the car for that. Besides, I'm too distracted by the addictive, bassy exhaust note when I put pedal to the metal to care what's playing on the crappy Clarion HU.
By the way, I need to lose 5kgs. No point having a heavy driver in a lightweight car :D hehehe...