Open scoop you can see the engine thru the top of the hood scoop.
Don't collect any of the common series cars you find a Wal Mart in hopes of cashing in later. There are thousands of guys buying that stuff up and putting it in boxes. I'm sure you have heard of the almighty Treasure Hunt cars. There has only been a few since '95 that are really worth or will ever be worth much. I'm not saying to leave them hanging if you see them. Just don't expect to make a mint. You can use ebay as a good indicator for the market on most cars. Sometime though, two bidders will go butt ignorant and pay way too much for a car. Usually two guys that are uneducated.
You would be much better off buying up cars, packaged or not, pre 1990. While there are long time collectors who have those years stored up, the nut jobs looking for a quick buck didn't get into it until around '95 or '96. Frequent yard/garage sale trips are a must. That is where you will find the best deals.
Some of your higher priced retail cars ($3-20) are good to get, but plan on keeping them for a long, long time before cashing in.
And you can always buy into the special edition online cars that Mattel does from time to time. They are high priced up front but are fairly limited in production.
The best thing to do in my opinion is to collect a certain car or certain series of cars that you and your son like. I used to buy anything and everything HW's related. Now I just buy the Mustangs. Go figure. This will help to not put a strain on your wallet.
Most of all, have fun. Don't look at it from an investment stand point in the beginning. Collect with your son until he loses interest (maybe he never will) and then look at values. Keep a running list of what you have, including a digital pic if possible, for insurance purposes. There are several collectors type software packages out there for the computer to help you with this.
If I can be of any more help just let me know. Happy Collecting!
M&M Member #685
Servin' the Lord in My Ford!!!