Guys

All of us have made an investment in our cars, wether it be a 10 sec mod'd or a base stock SE, we still put out the coin to own them.
If you bought new, you really dont have to worry about the last guys maintenance schedule. If you bought used, you maybe a little bit more leary about the services your GP got. When you think about services and maintenance you think of oil change, tranny service, coolant flush, balancing, brakes etc.
I recently went to the local auto parts shop and looked around at the different treatments you can buy- Oil treatment, fuel treatment, tranny treatment, etc. All had there own simple instructions and seemed to have very little cost to them.
My question is, Are these treatments just a cash grab or would they actually work to protect my investment? I have read the blogs about them, looked at the specifics and have seen comments going both ways, good and bad.
Is it worth doing for example a oil treatment the next time I change my oil? Throwing in a quart of fuel treatment (not injector cleaner) the next time I fill up or tossing a quart of tranny treatment in when I get my service?
My biggest thing is, protecting my investment. Be it that I bought used and even with going to the dealer it was bought at, they cant give me the info I want- just the basics.
What do I do? I have a service schedule and follow it to a T, but is it worth the extra coin with these treatments?

Thanks
Mike