I learned not long ago that "It's good for the smoker" is a lousy excuse used by people to justify harvesting less than desirable fish.
Simply put, what goes in comes out. If you feed the smoker junk (dark fish, long past its prime) the end result will be junk. If you smoke bright fish, with firm flesh and no visible degradation, the final result will be superb.
This is my standard for excellence when it comes to chum:
That fish is obviously from the ocean, and some fish of that quality can be caught early in the season in the Squamish river (not this year, though - no retention for Chum is in place). In the Vedder it is very unlikely to get a chum that matches those caught in the ocean.
Another thing to consider: once salmon stop feeding, a male salmon is much better table fare than a female salmon. The female dispenses a lot more energy to nourish the eggs in its skeins - to the detriment of its flesh.
It baffles me to see some of the fish that people take home from the Vedder. Some of them I wouldn't touch with a ten foot pole.