Lakers really needed to do something bold and getting Nash was bold. While I predict that he'll make a difference to that team (needing a smart effective point guard), whether or not it will get them into the Finals is whole other kettle of fish.
What the Fakers lacked in competing with Thunder in the playoffs was young athletic legs and a steady defense. Nash will add neither of those to the team. He does not play defense and in 4th quarter if they face next year's Thunder again, it'll probably get even uglier.
They still need a 6-10in to 7ft foward-center that dominates the boards and the other elite forwards or centers. Is it Bynum? Not-so-much, as his head is not screwed on straight. It could be Howard, but it depends on what Lakers have to trade to get him and then the chemistry of how he fits in with the remaining team.