Personally, I would save the money and go with CBR (preferred and don't let them "upgrade" you to a pirate room!) or a regular room at POR.
I would not spend the extra money on a Cars Suite with a 3-year old. We stayed in a Nemo Suite the first year AoA opened when my DS was 4 and he got over the theme after the first day. Then we were stuck in a big, but incredibly uncomfortable and loud room. The food court was also mass chaos. I will never, ever stay there again.
By staying in a regular room at a mod, you will spend less and get upgraded amenities. If you really want to experience the Cars area at AoA, you could always take a bus to AoA from one of the parks and walk around the Cars area at the resort.