My guess is that a "big mess," with things growing more closely together, maybe there's a better habitat for predators? I see a lot of lizards and geckos in the wilder parts of my garden.

I'd have to agree and say you guys got it right. I can't honestly think of any other reason! I guess with more cover, there's more hiding places for the predators to pounce from, so-to-speak. Whereas in a wide open area the lizards don't feel so at home. That's why you see them in the fenceline vines so often, more cover there. Those Cattle Egrets are a threat to the lizards too, depending on where you're at, so they would be smart to keep a low profile while they're out hunting!
Personally;
I noticed on my Tomato plants("Sweet 100 Cherry" & "Totem") that I have far less insect damage in the "messy" Totems than in my trimmed, nice-looking climbing cherries. Since I noticed the damage (those inch worms get to everything!) I've started spraying everything down with insecticidal soap(forget what brand...will look at it and name it)and it seems to be helping. I've even got a few nice tomatos and a friend across the street has some wonderful lookin Beefsteaks! (Now that we transplanted them and got the 'pillars off)
Now the Pak Choi, Romaine Lettuce, Sweet Basil, and the Radishes...that's a different story. The bugs were getting to those before I knew it, so I had to whip out that soap spray before I lost it all! The White Flies are fairly bad where I'm at(They love, and I hate, the Areca palms!) so I have to keep a watchful eye on everything.

The inchworms;
If you find them on your tomatos, or other plants, and don't want to kill them, transfer them over to some Green Ti, they'll eat it just the same and can't cause too much damage! If you prefer to rear them, it might be interesting as they turn into quite an interesting moth; have one that just hatched today, will take a photo and post it tonight!

I've got another insect related, relatively off-topic, request too. I'll post a new thread when I post the photograph on this one, I have to look up some images before-hand....Lol.

Hope this helps ya out a little guys! In the end, I don't recommend letting the garden go completely wild to control insects. Remember, if kept clean it's easier to spot the problem before it gets too bad...if it's TOO hard to tell the bugs from the plants, the damage is done before you even realize it!

P.S. I'm gonna hit you up this week Pueokai, promise! Lol. Talk to ya then!