Most important game of the season? OKAY. Every game is of the same importance in the regular season, and if you want to go with "oh well, you want to perform against team X, and Y" then the Spurs game was by far the most important game of the season. The Spurs are a legitimate title contender who have won multiple rings, the Mavs are a team that generally loses in the first round of the playoffs. With that being said, its the same importance as every other game, considering the Lakers almost certainly aren't going to catch either the Spurs or the Mavs, its just another game against a good team, more of those to come.
I'm sticking with my prediction of this road trip (5-1, only L @MIA).
This is the most important game of the season. We must win, remember how the Lakers blew the previous game @Dallas, no letdown tomorrow, let's get the W!