Gold does give more than silver, Then silver more then Bronze. Also there is a larger difference between Gold and Silver then between Silver and bronze. So choose your endorsments wisely.
Its common sense, its why if you pay attention to the endorsements you pick up in game (speed) you'll the the bottom right go (If you dont have any speed endorsements on) Copper/1 for the first one and you get a little faster, silver/2 for the 2nd one another increase in speed, and gold/3 on the 3rd one and you'll be at a level 3 speed endorsement speed. Its also why the actual products change in the custom class screen as you move down levels. Its done that way so that you think and prioritize when assigning endorsements to custom classes.
You can also check this by changing what level the clip size endorsement is as, at level 1 its barely noticeable at level 3 on the gunner its double the ammo. Same with reload speed, there are big differences based on the levels.