Hmm. I guess I'm going to live with the software fix for now, as I don't trust my soldering skills. I can deal with drive upgrades, but soldering irons and I don't mix with good results.
As for the so-called strange behavior where the empeg powers up immediately upon connection, I don't think it's a software thing, because, of course, the kernel isn't loaded until it boots up. I'm guessing the power circuitry uses the leaf switch in the adaptor plug to decide whether it should power up right away (if it thinks it's in AC mode based on the leaf switch) or wait for the key to turn (if the leaf switch tells it that it's in the car.) So I don't think we'll be able to have any kind of software fix for that particular piece of the puzzle. If I'm wrong, someone will correct me, but I don't see how we could fix that in software... I'll have to learn to live with that (not a big deal) for now.
What is a bit of a bigger deal is that, unless I screwed something up when I tried it out, it doesn't seem to power off when the standby timer has expired, probably for the same reason. In the power circuit, it probably figures "hey, there's an AC adaptor plugged in, why should I power down?" or something. That means that when I turn my engine off, it correctly goes into standby, but it never powers off like it does with a properly functioning adaptor plug. At least that's what I'm seeing.
But in the win column, I did find that lowering the TUNER_TIMEOUT to 2000000 gives me proper tuner detection every time, without an excessive delay when I plug it in at home. So for now, your fix is exactly what I need, until I get the guts to solder a new plug on, or decide to send it to Cambridge. I'm kinda upset that this has happened to both of my empegs, but life goes on. My guess is that more and more people will be seeing this as their empegs get into their golden years.