When fishing spinners for salmon, my experience has been that you want to fish them as slow as you can while still keeping the blade turning over and not dragging the bottom. As for telling a bite from the bottom or a line bump from stacked fish. The bottom will be a tap or a dead stop, in heavy current sometimes those taps will feel pretty hard. Line bumps will be taps that have a little life or movement to them occasionally you will get tail slapped which may feel like an aggressive take with no hook up. When a fish takes it will vary from your bait stopping to a gentle pulsing tug that has life to it not dead like the bottom, and it will have a longer duration than the fraction of a second line bump. Sometimes you get lucky and and a fish will freight train it and pretty much set the hook for you.

Now, IMO the reason most inexperienced anglers ask 'what does the bite feel like?' is not because they have felt bites and didn't recognize them. Sometimes, especially for steelhead they are fishing the wrong water and then get discouraged when others are having success and they are not. Another common mistake I see is guys not maintaining contact (feel) with their bait. They cast too far upstream and allow slack and belly in their line and by the time they would feel a bite the fish has let go, and if they do feel it and set the hook they can't get the slack out to stick the fish. IMO you should try and cast as close to across current as you can, sometimes you have no choice, but I try not to cast more than 15 degrees upstream.

If you are not having success pay attention to those that are (make sure success= fish hooked in the mouth). Take notice of what they are using the characteristics of the water they are fishing and their presentation. Be patient when fishing crowded areas and fish with confidence.

I hope that helps.