Define 'wasting your time'.. they come in with the incoming tides... so timing is an issue. Of course as the water gets higher, the water moves slower - almost to the point of backwards - your spinner (if that is what you are using) spins slower or not at all if too big / heavy.
They also travel upstream at different speeds. Subsequently, once they get beyond the tidal boundary (way past Mission), they are now scattered throughout the river as opposed to a 'school'. To answer you question - better results would be attained further upstram beyond the tidal waters.
However, saying all that - last year, when the pinks were in, I got to the river midday and noticed the tide was almost as low as it could go. I had an hour to kill and figured why not. Decided to use a #3 blue fox and 15 minutes later hooked on to a 12 pound red spring.