I suspect Jon and Walt missed my point about the power of a modular, connectorized Plug and Play design being able to minimize aircraft down-time. Yes, the actual panel fab time doesn't change very much, but the all-important aircraft down-time really gets a boost from a modular approach to avionics and instrument panels.
In an aircraft designed for modularity, avionics upgrades can be fast and relatively easy. In an aircraft that's already connectorized, a pre-fab panel can be installed very quickly - yes, a weekend is entirely do-able to get the new panel in and lit up. If one applies some forethought, the panel itself can be designed to be modular, with connectors in strategic locations. As an example, when the audio panel was initially installed in a basic VFR panel, all the ins/outs for COMM2 and NAV2 could have been wired to, for instance, inexpensive DB9 connectors - installing a new radio using a pre-wired rack can be done quickly because one no longer has to dive into the audio panel wiring. Similarly, from a mechanical perspective, if the panel is built as a mechanical frame with removable bolt-on inserts, the mechanical installation can be pre-fabbed and ready to bolt into the airplane.
I agree that an airplane that was put together using straight point-to-point wiring is going to take some time to modify to a modular design, but once the aircraft side of the wiring is on connectors future updates can go very, very quickly indeed. If you're not already selling your customers on the value of modularity, now might be a good time to start. The real value is in the way it reduces aircraft down-time when doing future upgrades. With the rate of innovation and change in experimental avionics, the payback cycle for designs built with modularity in mind is short!