Yes, unlike the analog signal from a wireless computer, the digital signal from the ANT+ should be impervious to interference from an LED light circuit. I've looked at the Cateye Padrone Digital and its Bluetooth sensors, which seemingly would also answer my wants. Thing is, by the time I buy the Bontrager or Cateye digital computer and sensor, I'm well over the cost of a GPS-based odometer+trip meter+speedometer and most of the way to a Garmin 130+. Yet all my wife wants to know is how far she rode this ride, in total, and maybe how fast she's going.
For me, part of the charm of the RIDEtime Elite is that it really is a lot like an old-school cyclocomputer, but with ANT+ sensors. It has a fairly large LCD display that is sufficient for me to read without wearing "readers" eyeglasses, runs on a coin cell battery that lasts a long time, and can be used day-to-day with very little user interaction. Nothing to charge; nothing to turn on/off. It's configurable enough that, for some users, it can be "everything that they need, and very little that they don't".
I've picked up a couple of the RIDEtime Elites on eBay for lower prices than normal retail. The older RIDEtime (non-Elite) units often go for much less, and might be suitable for your needs. If you got the right deal, and if an off-brand speed sensor worked OK with it, you might be able to come up with a package for a lot less then normal retail pricing of a RIDEtime Elite + Garmin Speed Sensor 2.
I was hoping someone knew of a basic wired computer with a wire at least twice as long as normal. Maybe there's not one.
Until I decided that I wanted to see cadence information, I was very happy with my CatEye Velo 7. If cable length were the problem, I wouldn't be afraid to cut/splice/heat shrink to extend the cable on one of those.