There is a time for trading up. But the statistical evidence strongly suggests that generally the better course of action is not to trade up, but rather to try to obtain more draft picks. The reason is that every pick carries a certain risk--some statistical possibility or probability of failure (which can be defined based on how high the draft pick is)--and that even the best in the scouting community know that drafting is really hard, much like hitting in the major leagues. If the objective for a batter is the number of hits rather than batting average, then the hitter is better off hitting .250 with 100 at-bats rather than .300 with 70 at-bats.
Every NFL team has the statistical information showing the statistical likelihood of drafting a Pro Bowl player, a multiple-year starter, a marginal starter, and a bust by draft number and by position. And if you work the numbers, they show that generally teams are better off with more picks than with fewer picks. Again, I offer as examples Marcus Davenport, Cesar Ruiz, Payton Turner. And again, these examples show not that the Saints do a poor job drafting players, but that drafting players is hard even for the best, and that it is arrogance for general managers to believe that year after year they can do materially better than most of their peers in drafting players.
Indeed, I would suggest that the teams that do the best in drafting do not necessarily have better player-evaluation information, but are better in applying the player-evaluation information they have--they have had in place certain offensive and defensive systems, and draft only those players who fit the systems they use. In short, they pick not the best players, but the best players for their team.
An argument I have pushed against in this forum for years is that the Saints are so good and deep that they don't need many draft picks--that is, why draft players you are going to cut in their first two or three years. Last year, the Saints had for them a typically low number of picks--five, which was the same number the Eagles had (though the Eagles traded away draft capital with Tennessee for A. J. Brown and with the Saints for future picks). But some good teams had plenty of picks: Baltimore and the Giants 11; Kansas City and Minnesota 10; and San Francisco and Dallas 9.
And I would argue that because of years of having so few draft picks, the Saints are not a very deep and mediocre football team (what would our over-under number be were the Saints not in the weakest division in the NFL).