Just a thougt but you still have time to get out now and still have fun with your kids with the cars that you do have and just buy new ones when they are with you and you want to give them a treat.
Many of the members here I am sure have been in the same position, myself included, your kid is 2 - 3years old, you watch cars (the good one) at least 7 times a week and he/she takes their cars to bed, in the car, in the bath (no lightning cannot swim), you can't go anywhere without Lightning and at least 2 other cars in your pockets. You spend a weekend converting a train table into a race track and act out the scenes from the movie especially the Frank scene.
That's the fun times and worth every minute we spend in the stores looking.
Then they get older and somewhere around 5 years old their wants and needs change and you may find that you are only collecting for yourself. You buy Lego, Super Mario, Batman or what ever they are into but still buy cars because you started and you still follow this web-site, you see the new cars coming out and so you can't stop, then you spend your spare time chasing cars all over the place (because it's now your hobby).
One day you will go into the garage and find boxes and boxes of cars that you have no idea what is in them and your kid may not even care that Lightning has travel wheels or TRU has a new metallic Miguel.
This is only my thoughts, but if I were doing it again tomorrow, I would try to get the main charachters and only buy cars when he was with me. I have no idea how much we have spent (time and money) on cars over the past few years but I quite sure it is a vacation or 2.
Also MN is not very good for cars.