First off, nice set of wheels you have there - the car they are riding on ain't too bad either
Now, on to your questions. Paul covered most of it.
CIS once warm uses 2 things to control the amount of fuel going to the engine. (During warm-up there's a few other things in play) The more air into the engine, the higher the plate. The higher the plate, the more fuel goes into the engine. The air-meter is funnel calibrated to ensure that when set properly at idle with the right control pressure the proper air-fuel mix is provided for the various operating condition (this is why you don't want to swap the air-meter/fuel regulator without checking first).
The other side is the control pressure (CPs) which counter-balances the air metering plate. Higher CPs result in leaner mixtures because the counter-force on the plate is higher. The lower the CP, the richer the mix. The CP is controlled by the Warm-up Regulator (also called CP regulator in some Bosch material). The WUR provides warm-up enrichment and then maintains the proper pressures once warm. In pre-80 CIS, the WUR also has a vacuum adjust that provides a leaner mix at partial load (fuel economy & emissions), and a richer mix for higher loads (WOT).
The later CIS used a Lambda system (yours included). There are 4 main components - an exhaust gas O2 sensor, a computer, a 35% throttle position switch, and a frequency valve (FV). The frequency valve reduced the control pressure. The Lambda had two modes - open loop and closed-loop. The open-loop system ran the FV at about 70%, providing enrichment for either increased load (throttle > 35%) or warm-up. In this mode it ignored the O2 sensor. In closed-loop, the FV is pulsed as necessary to achieve proper AFR using the O2 sensor for feedback (generally 50% duty cycle). This functioned much like the vacuum-adjust WUR but more accurately, especially if out-of-tune.
As for warm-up, your WUR was calibrated to have the additional enrichment provided by the Lambda, but if your car is working now w/o the lambda hooked up then someone has already modified your WUR (or replaced it with an earlier model). Additionally, the extra cold-start mods in the later CIS systems weren't tied to the Lambda, but rather the air box assembly, so you would have to change that too.
So, what does this all mean to you. Well, without the vacuum adjust WUR or Lambda, you won't get the fuel economy benefits at partial load w/o risking being lean at the top end. If this is a weekend fun car then no big deal... if its a daily driver then the decision might be harder. Additionally, if you want to re-add the lambda, match the years.
Just note that you won't be able to use the Bentley guide to set your control pressures as they will list the CIS + lambda specs.
Personally, I wouldn't mess with it. I have the pre-lambda CIS and it works well enough. Your vehicle should be emissions exempt pretty much everywhere, and it won't increase performance or drivability in any meaningful way.