The chance of getting an impact player in the first round is way higher though, so trading them away all the time wouldn't make any sense to me.
This statement of "way more" is backed up by what?
Looking at my own records of Packer draft history since 1980, the Packers have had the following success rates in each round:
59% First Round
58% Second Round
39% Third Round
41% Fourth Round
29% Fifth Round
39% Sixth Round
25% Seventh Round
In a hypothetical situation over ten years, if the Packers kept each original draft pick in each round, their average draft success would be:
6 successful 1st Rd drafted players
6 successful 2nd Rd drafted players
4 successful 3rd Rd drafted players
4 successful 4th Rd drafted players
3 successful 5th Rd drafted players
4 successful 6th Rd drafted players
3 successful 7th Rd drafted players
30 Total Successful Players out of 70 draftees (43%)
The Packers average 1st round draft position is 17 which is worth 950 points in the value chart and worth more than 2nd (430 value), 3rd (195 value), and 4th (72 value) round picks in the middle of each round. So assume you can trade a 1st for three picks. If you now trade your original 2nd round pick - assuming middle round value of 430 - then you could again assume getting in return a 3rd (195 value), 4th (72 value), and 5th (34.5 value).
We these extra picks in that same ten year span and using the Packers same historical success rate, you get:
0 1st Rd drafted players (first round picks traded for 2, 3, 4)
6 successful 2nd Rd drafted players (second round picks traded for 3, 4, 5 - still have 2nd rounder from above)
12 successful 3rd Rd drafted players (two extra 3rd round picks in each draft)
12 successful 4th Rd drafted players (two extra 4th round picks in each draft)
6 successful 5th Rd drafted players (one extra 5th round pick in each draft)
4 successful 6th Rd drafted players
3 successful 7th Rd drafted players
43 Total Successful Players out of 110 draftees (39%)
Over ten years of trading away your higher picks and assuming the same success rate in each round (and obviously finding trading partners each year), you will end up with 13 more quality players on your roster and will not have paid as much in rookie salaries. Plus, with a greater influx of potential contributors each season, a team could be more willing to let its elite players test free agency, thus saving cap space and team dollars.