The major change of course was that they lost Bobby Holik who was probably the team's best forward in 2002. But yeah, the 2002 Devils were +553 shots overall, 2003 they were +672, with a lot of the difference likely coming because of penalty differential.
No, that Sykora trade didn't work out that well - the Devils ultimately ended up with 2 years of Friesen, 1 year of Tverdovsky, and a 3rd round pick (who subsequently didn't sign with NJ). Of course the Ducks only ended up with 2 1/2 years of Sykora and they dealt Sykora and a 4th for Maxim Kondratiev, so maybe the trade didn't work out for both sides from a pure asset perspective.
Of course. Missed saying Holik was gone. So you lose your best forward on a below average scoring team. You really don't get a great season from Nieuwendyk. No young player comes in and steps up offensively (Berglund and Bicek combine for 9 goals in 82 games). Elias and Gomez have down years offensively. None of them find much chemistry with anyone all season. The real upgrade was the great season by Langenbrunner. All that and the team slightly improves offensively.
But it goes to show, you have a good goalie and a great defense, you got a very good chance. It really helped that the Devils not only got hot, but ran into the opposite of Irbe/Weekes 2002. You got some Steve Shields in the 1st round with the Bruins. Then Khabibulin crapped the bed in round 2. Second straight series with a goalie change mid-series. In round 3, Lalime was pretty awful. Ottawa was the better team by far, but Lalime killed them in that series. Finally, Giguere, after being so good, was really crappy in the Finals. Got beat on a ton of bad goals.