The IR sensor chip from the Normal Wii remote could also be used as a IR homing sensor for Manpads with only the addition of better focus Optics

Car radar decetors are all so old-fashioned these days since the world is full of diverse threats. IR/Laser as well.

I want to build a modern RWR into my car and start profiling all the ELINT around me in 360 like "hey that's a volvo coming over the hill" rather than just beeps.

MAN-Portable Air Defense (System). Basically a tube with optics that you can use to fire an anti-air missile from your shoulder. Stinger and Strela are some examples

The sensor is just a 128x96 monochrome camera and it's fairly trivial to programmatically determine where IR lights are at in the frame. The processor just needs to scan through 12,288 pixels, find the center of a cluster of bright pixels and return coordinate. It's not a complex operation, but the devil is in the details: I suspect you would still need to overclock the hell out of it to process over 60fps. Manpads are fast with the Stinger clocking in at about mach 2. As the missile gets closer to the target, it wouldn't take much of a delay to screw things up.

So sure, if you spend the cash on a quality glass, you could do a ton with that sensor. It's probably years ahead of what was on the original Stinger, actually.

It might work, but the use-cases are extremely far apart here.