DrRollo, Please dont take this the wrong way. But its been seen numerous times before on here and renaultsport that peoples belts are snapping and failing PRIOR to the 5yrs some even 3yrs. Regardless of what renault put on paper, the failures are occuring and at great cost to those individuals. I understand its money that you dont want to pay, and by having something in writing it will put your mind at rest somewhat, but its still going to be a risk regardless of what renault state what/when is due.
Your at 3yrs and at 18k miles. You probably dont need it to be done quite so early, but the key word here is probably. Its not just engine milage that affects the belts its just general weather and use etc.. so the risk is still present regardless of your lovely low milage example.
For peace of mind, I PERSONALLY would get it done when funds allow, as its be proven again that renault will not incur any cost if the belt does snap. If money is tight, which to be fair even if it isnt, its still an awful lot of money to spend just on changing a belt.
With your track days etc that you have done or do, i would sway more towards getting it done just to feel 100% confident in my/your car.
Whatever you decide, good luck.