Lots of great discussion and interesting stuff here!
I have great news! I found the problem. Saggy flippers. Flippers are in very good (not perfect) condition, but rested about 10 degrees below the line that the rails make. I adjusted them to look like the PAPA machine, which is parallel to the line the rails make, and all the ball handling skills I've learned with the flippers suddenly pay off two to three times as often! Used to be if it bounced twice on any combination of the flippers, it was going to drain and would be nearly impossible to touch with the flippers. Now, twice is more common, and you can still manage to tap it to the opposite one if your timing is good. Live catches don't end in split second chances before draining anymore - you've actually got a few moments to choose your position before launching the ball again. The outlanes are still ravenous, but the center isn't the same black hole it used to be.
Also, I switched it to 5 ball, liberal. It's not as fast-paced and exciting because the lights aren't flashing back and forth on the pops anymore - just switching from lit to unlit and back to lit periodically with the 100s. But at least when you have a crappy game it's longer than 45 seconds, and generally still beats 1000. A crappy game on the 3 ball always made you feel completely incompetent.
I do have it set quite steep on standard length feet. Seems to give similar feeling of gravity to the PAPA videos. Slings and pops are all in great shape, and nudging while the ball is on an upper sling has always made the upper banks possible to do very quickly if you get it right. Love doing that!
My machine was missing the pins at the top of the return lanes when I got it. When I got replacements and put them in, it seemed the overall change was positive, but bouncing off the wood sides is pretty much out now.
My wife and I have put new high scores at 6400 and 6700 and, while feeling a tad slower paced, the game is much more satisfying to play. I fully recommend 5 ball play on it at this time!