I don't think you missed out on an early retirement, but usually the "three track" type of equipment is Lionel "O" scale. It's probably worth more than the price paid in 1976, but don't loose any sleep over it.
I'll start with the smallest and move up. Z scale is the smallest and the newest. It's 1/220 scale which means one foot equals 220 feet. The next is N scale which is 1/160. The next is HO which is 1/87. S scale is 1/64 O scale is 1/48, On30 is the sm...
Mel, I would post this question on one of the forums @ trains.com. It's an excellent site with lots of knowledgeable people. Rob