Austin Collie and Early Doucet are not going to decide the NFC West race. They might not even earn spots on their new teams' 53-man rosters, let alone spots in the receiving rotation when games start counting.
2009-12 Doucet vs. Collie (3rd down)
But with the 49ers adding Collie and the Seahawks adding Doucet, I've found a parallel to satisfy your need to sustain the rivalry narrative. The chart shows their their third-down numbers since 2009, when Collie debuted with the Indianapolis Colts and Doucet was a second-year pro with the Arizona Cardinals.
Both Collie and Doucet where primarily slot receivers on third down during that time. Both are 6 feet tall, more than 200 pounds and lacking in top speed by NFL standards for the position.
Arizona released Doucet this offseason after firing coach Ken Whisenhunt. Collie last played for Indianapolis in 2011, when he suffered a season-ending torn patella tendon.
The 49ers and Seahawks have lost receivers to injury. Options on the free-agent market are scarce this time of year because the roster limit is at its 90-man maximum. Teams tend to carry about 12 receivers on a 90-man roster (384 total if each team had exactly 12). Most of the best ones already have jobs, in other words.