You beat me to it. This is going to be a popular thread, i.e. 'starting the debate'.
I just got the kit because you only live once, so 'why not?'
The NP is a great car. The SS just adds a bit more to it with throttle response etc..
It's never going to be a Ferrari 355, so don't expect miracles. This is a sub £20K car and it's superb fun for that price bracket.
I guess a lot of this, like most things, almost everything actually, comes down to money.
Sorry to go off-topic a bit here.
I understand most people's opinions. If £2500 is a lot of money to someone to fork out and you want the extra power the engine is capable of, without the extra wheels and a wooden crate, then a remap is probably a good option. But you have to take into account the other factors, like warranty, re-sale etc.
As I said in another thread ages ago, money is relative to whatever else you do in your life. If you don't earn a lot and your car is your P&J, then £2500 is a lot of money to fork out, so other options are worth considering.
If you're intending to keep the car for quite a while, like Draigflag says, the £2500 divides into a small monthly amount, like £40 a month over 5 years, so it's up to the individual to decide whether it's worth it.
rant over...I'm off for another Cointreau...