What is it about a 911 that makes it the only car that always seems to have a lean problem and not ignition? Could it be because the ignition wires are too pretty or too expensive to be the problem?

The fact that it starts fine if I lift the air meter plate tells me it is a gas issue, not ignition. And I already rebuilt the distributor, replaced the wires, spark plugs...Plus I've got a boat battery in there for that extra kick in cold weather ;).

Here are the symptoms:

1. Does not start well in cold weather (takes at least 10s cranking)

Try disconnecting and grounding the red/black wire at the thermotime switch and a cold start. If no change, you need to remove and test the CSV.

2. Sometimes will stall with a pop a few minutes after driving cold. Will not restart unless I give it more gas by lifting the air meter.

If the engine is below 113 F, see above.

3. Gas mileage is down by about 2 mpg.

Unless this was measured under a controlled situation and several hundred miles, it could be a million things, including the weather and what you had for lunch.

4. There is a very annoying vibration noise linked with the throttle, when the car is under load. Same rpms in with clutch in makes the vibration go away.

A vibration is something you feel and a noise is something you hear, you need to separate them to isolate the problem. CIS makes a rattling noise based on the amount of fuel run through the injectors. Some people confuse it with pinging, because of the way it reponds to throttle input. Same rpm is OK to test an imbalance problem, but not pinging or the CIS rattle. Eliminate the pinging issue by retarding the timing or raising the fuel octane.

Don't lose track of an important clue - the rattle. Sounds like detonation from a lean engine to me. Check those WUR pressures.
Yes, the engine will start without the CSV. Just pull the thermoswitch connector and you can readily verify that. Even a cold engine will start - not readily, but it'll start.
Finally, the fuel distributor doesn't squirt when the pie plate is in the rest position. But the engine doesn't need to be running, just rotating (e.g., under the starter) to produce sufficient vacuum to lift the pie plate. Think about it a little and you'll see. Or, pull the air filter, turn the key on and listen - no fuel flow. Lift the pie plate the tiniest bit and it'll squirt.
The CIS is a pretty good system, even in the EFI world today. It's the lack of replacement parts that is killing it.

good advise from paul.

control pressures need to be checked.

lifting the AFM plate, when cold, can indicate 2 things, CSV or cold CP to high.