Renault Laguna fuel sensor

Engine starts and runs good but when hot and you come to temporary rest, say traffic lights, warning lights come on and revs are then limited to 1900. If you switch off and restart the car then runs OK
Had the fault diagnosed as petrol temp/pressure sensor which puts engine into limp mode when detected hot. Friendly mechanic at Renault says this is a common problem with this car and age , need to replace sensor device , part cost £250 and £250 to fit/fix and then no absolute guarantee it will last more than a year. Question is, is it worth doing it. Does anyone else know of this problem? is it fixable? Mechanic say Renault know of this problem and after many part updates have thrown up their hands in desperation. HELP