To be honest mate, if that was me, I wouldnt pay it and take it out. In essence you are doubling your premium for a nitrous kit and 25bhp. That's two fiesta RSTs with mods up to 200bhp declared for the price of one with a 25bhp shot of nitrous.

And as you say 31 y/o with full no claims and the rest of it. Not worth it in my eyes.

On another note, I'm always in and around southgate. Never seen a red RS though. Whereabouts are you close to?