In my opinion, it depends on what the rest of your team looks like. The last 2 years Lynch has been a back and forth back who seems to get dangerous towards the end of the season. In my experience with my league I have always traded for Lynch at about week 4. I happened to draft him this year and don't plan on getting rid of him. St. Louis has a very very good front 7 so I wouldn't judge the week 1 for the rest of the season. Cooks has a great match up of course this weekend, but I think the NO line has some problems. I think everyone has been looking for the a great Raiders back for the last 5 years, but none are consistent. If your desperate for a WR, (and I think Cooks is going to be getting a lot of attention each week because who else?), then maybe. But I would ask for a different back, seems like they are trying to give you Cooks for Lynch, just address your needs for your roster for player like Lynch. Good Luck with your season!
Quick Edit: I would wait to see what Lynch does against GB. Forte just ran all over them with Chicago's O-line. If you want to unload him, do it after he has a good week.