I doubt you need the WP because of the low mileage but remember things do deteriorate over time.
One thing.... It doesn't matter how many miles on the car when you change the cam belt you MUST change the tensioner and idler! I've seen it twice now where an old tensioner chewed up a brand new belt and one was on a low mileage car like yours, maybe a bit more, about 35/40k.
Just so you know, main dealer will be competitive on this job. I paid Lexus to do my cambelt, tensioner and idler and it was £320 all in. I didn't do the WP and mine was on 80,000 and I drove it for 2 years and sold it on 107,000, no problems.
Also belts should be changed every 60k or 6 years. Your aux belts may look in good condition but you can't tell by looking, nobody can. Change the lot, also aux belts at Lexus cost me £50 for all 3 fitted.