The example you use with Lett is not relivant. In the Super Bowl years, the cap had not come into play yet. In those days, you could sit players on the bench. Now, you can't.
We don't know that teams aren't interested in trading for Walker, if Green Bay elects to intertain trade offers, I suspect they will get interest. If you think WRs are not valuable in the NFL, I would recommend you look at the last 8 to 10 drafts or so.
In 96, 11 WRs were taken. 5 in the 1st and 6 in the 2nd.
In 97, 8 WRs were taken. 4 in the 1st and 4 in the 2nd.
In 98, 10 WRs were taken. 3 in the 1st and 7 in the 2nd.
In 99, 5 WRs were taken. 3 in the 1st and 7 in the 2nd.
In 00, 8 WRs were taken. 5 in the 1st and 3 in the 2nd.
In 01, 10 WRs taken. 6 in the 1st and 4 in the 2nd.
In 02, 11 WRs taken. 3 in the 1st and 8 in the 2nd.
In 03, 8 WRs taken. 3 in the 1st and 5 in the 2nd.
In 04, 10 WRs taken. 7 in the 1st and 3 in the 2nd.
In 05, 10 WRs taken. 5 in the 1st and 5 in the 2nd.
Over the last 9 years, 91 WRs have been selected. That's just over 10 a year in the first two rounds. 44 1st round or almost 5 1st round picks a year and 47 2nds or just over 5 a year. This has been going on for almost 10 years. This would suggest that teams are drafting WRs high and it's not going to stop. It also suggests that all the WRs being drafted are not panning out. All the more reason to get a proven commodity if you can.
Bottom line, Ellis and Glover will be of no value to us in the next few years, IMO. Better to get a good young WR that can be a franchise type player for you if the opportunity presents itself.