I have 3 machines now and Taxi is definately still my favorite. I like the Williams system 11's because there is lots of parts for the mechanics for the machine, NOS and remanufactured. They are pretty simple machines, and if something goes wrong with them, you can fix them yourself, or learn how to pretty quick! AND they are fun to play! I have a Taxi, Police Force and Fishtales and play them in that order. My taxi is a Marilyn version and I have looked on the internet for hours and hours and still can't really find out too much manufacturing details about the machine. All I could find is that there was about 7-8000 total machine made. 1-2000 were Marilyns and most of them were sent out of country (US) because Williams sent early production machines overseas and out of country first before the suppliers to the US. They did this with EVERY model of machine they made. Also with alot of production machines, they were 'secretive' on production amounts! They would have serial numbers start out a certain number, then they would totally change the number so if you were to log the numbers in sequence, there was no real pattern. To confuse competetors? I don't know. Don't really know how that would benefit a company keeping production amounts secretive? Maybe for a collectors factor, but other than that it doesn't make sense to me. If people are buying the machine you make more! If this machine were to be worth some money some day? Who knows. I collect and restore machines for my own personal enjoyment, not to make money.
Anyways, I have restored my Taxi to near mint, and have done a few mods to it. I put a video of it on Youtube if you want to have a peek. I took the traffic light mod off of it since the video because I didn't really think it suited the game properly. It was always on and I hacked it into the power supply board. Just wanted to keep the machine real, with no hacks, and I didn't like it anyways. This machine will be a keeper for me FOR SURE!
Once you restore your playfield, just keep it waxed once in awhile. I use pure CARANUBA wax. I have a bottle of that Mother's pure Caranuba wax, and it works awesome! Everyone will have their own opinion on what to use for playfield cleaners and wax, but all I do is dust the playfield with a very damp cloth, then I wax it. WAX ON WAX OFF! Just like the Karate Kid movie and the game KICKS ASS! Lightning fast play and looks great! A good final touch is to get a new piece of tempered playfield glass too. You can get a new piece for anywhere from 30-60 bucks. I live in a bigger city and there is lots of local glass guys here to shop from.
Good luck on all your restoring! I enjoy it and it's rewarding as well!
Here's the link to my video on Youtube make sure you watch it in HQ! (click on the high quality button on the video!)

I recently watched that 'TILT the battle to save pinball" DVD. Its pretty interesting. They have a segment with interviews from EX Williams employees on there and they all said that a big chunk of Williams sales were with this company from Germany (30-40%?), so they would ship all the first production machines mostly there and elsewhere overseas first before anywhere else. There is a factory tour and lots of other cool info on there too! I would recommend buying the dvd for sure if you are a pinball freak like me.
As for the spinout skill shot in my Taxi game. Well you have to have the plunger and the first ramp that carries the ball to the spinout in a perfect alignment in order to get good revolutions on the ball in the spinout, but good luck on that. Usually you just have to shoot the ball as hard as you can to get the top spinout score! I found out that operators were putting plungers with a sharp point on the tip of them so you couldn't hit the plunger with your palm as hard as you could to get the top spinout score. They did that cuz the spinout ramps would get badly damaged from 'palming' the plunger. I am not sure if Williams did this or if it was an aftermarket thing from somone else?! I know that this "hit the ball as hard as you can if you want to pierce your palm feature' was on quite a few pinball games that I have played.