This is a legitimate view, but you also have to ask yourself, "Do you want a prospect who has never played in the NFL, or would you rather have a guy with a proven track record who also already has chemistry with your starting QB?"
Once upon a time, I criticized the Rams for doing this with some of their trades for veterans and I've seen now that I would rather have a young veteran nearing or in their prime over a dice roll who is much less likely to work out.
I think the need was pretty large..the Cardinals almost had to walk away with a receiver and Brown at least won't cost $20+ million for two years, which is the going rate for a good starting receiver right now.
If the prognosticators are correct with how much the salary cap will grow over the next 5 years, a lot of these complaints will seem trivial real soon. I expect we'll see OK QBs making 40 million, Superstars making 55 million, and top WRs over 30 million. For years, I've thought WRs were a bit devalued and it looks like the NFL is finally starting to value WRs like they should.
If I'm a GM, I'm stocking up on WRs and moving on from them regularly...ala the Steelers approach.