I think that's a bit too simplistic.
First, the goal is to be a good team, so we want our 1st-liners to be above average. If you have 3 guys ranked in the 50s or 60s for your 1st line, odds are you aren't going to be very good unless your depth is exceptional. That isn't likely to be true if we trade too much of what we have. Finding top talent is difficult, and expensive. Most likely, there just isn't a deal out there. We probably need to rely on depth more than power at the top, as well as the kids taking a step forward. That means trying to figure out why most of our team took a step back this year.
Secondly, we need to concentrate on goal-scoring rather than just points. One major problem this year is that in terms of goal-scoring, Datsyuk and Zetterberg are very poor relative to the top forwards on other teams. The rest of the team, even having a poor year, is average or slightly above.
Of course it's simplistic; I said myself that it was one crude measure. The point is that the Wings don't even have 3 below average first line level players. They have only 1. Relying on depth is a myth; if you look at Cup-winning Wings teams, they all had top-level first line players (I only glanced at total points and not PPG). If a team doesn't have top-level players, depth doesn't truly exist. I think this season is bearing that out; without primary scoring, secondary scoring doesn't matter.
There isn't much of a difference goals v. points. If players are putting up points, it means someone's getting goals. If someone is scoring goals, it means others are getting points. Detroit's 3 best at PPG average a rank of 88 in the NHL (Datsyuk is 43, Z 108, and Larkin 113). Detroit's 3 best at GPG average a rank of about 82 (Larkin is 71, Datsyuk 86, and Tatar 88).
I think the Wings have shown a good propensity to find 2nd line level players. I would be very willing to give up some of those for higher-end talent. With extra playing and power play time, the Wings have guys that would probably step up to produce sufficiently at the 2nd and 3rd line levels, especially next season. But of course, it is easier said that done, as there has to be a team willing to give up higher-end talent for more depth.
Of course nothing is that cut and dried, but I understand your point. On that you are correct. Not enough top line guys. There is always a debate on are you better off with 2 good players or 1 great player? If you have 2 guys (Nyquist and tatar) that combined score 40-45 goals and make 8-9 million per year is that better than having 1 guy that scores 40+ and makes the same money? The hard part is the answer changes based on your team. If your team has 3 super stars then moving one for better depth makes sense. But that isn't us atm. We lack the stars so we need to trade/sign/develop some.
The thing to keep in mind is that it isn't just looking at goals by 1 new player v 2 others. Chances are there will be another player or two that come up with more goals now that they get more ice and PP time with the other 2 secondary scorers away.