Near the beginning of Cavern 4 there are some hidden rooms to stock up on large amounts of dynamite and ladders in exchange for gems. Going through the passages nets around 1100 points every 2-3 seconds. While the points might not be as much in one shot as the other solutions, I found it more efficient because I didn't have to frequently load the game to net the points. You can see the spot I am referring to in the following video at about the 55 second mark, give or take. Also, it shows the hidden warps on the first three caverns to get there quickly, in case you forgot to save the game initially.
I had about 300K to go and got it somewhere between 10 and 20 minutes (sorry, I didn't think about actually timing it until I finished).