If you think the existing speakers are fine , that's great, just I found them a worthwhile mod, and not too dear. The standard head unit does seem okay.
My remap was £360 and they came to my house and did the necessary. Yes, it is noticeable and very smooth, with no foibles that I've noticed. I had the remap done to atke into account my DSG gearbox, which has a reported torque limit, so its backed off a little from the manual box version, I understand. So no clutch slip on mine, though with the DSG, I'm not sure what that would feel like, as it uses 2 wet clutches in its system.
Overall worth every penny, TDi remaps are about the best bang for the buck out there in my opinion and it doesn't just affect top end, but improves subtly across the whole range.
If I bought another TDi, it would be a no-brainer, would have it done straight away.