I recommend going for this branch last, as the "Lantern's Light" ability will cost you a cool 100,000 points, and will not be purchasable until you reach level 10.
The way I ground the last 130,000 xp I needed was by playing the Mission 10 on Poozer UP UNTIL the final boss, once the cut scene for the start of the fight began I'd quit out and then start Mission 10 again. I found that I got about 6-7k points in about 4-5 minutes without too much difficulty. Mission 2 on Emerald Knight isn't bad either, but it only gives you around 4.5k in the same amount of time. If you feel up to it, you can replay mission 9 all the way though on EK again, as I racked up about 75k through the whole Mission. However, I found using Mission 10 allows you to get into a rhythm because you can skip all but one (short, 5 second) cut scene, there are no lulls combat, and the confined spaces allow you to use your constructs to good effect, as well as rack up combos. It also takes a considerably less amount of time than playing though full missions. Turn on your playlist/podcast of choice, and a little over an hour later later you'll have this and your Big Spender achievement.