I've done some playfield restoration. I'm graphic artist and screen printer by trade. I've gone as far as screen print directly onto the playfield to duplicate detailed lacework. But this is what I do everyday except is on other products.
#1 is color matching. A perfect restoration starts and ends with color matching. It must be perfect or even the best work is wasted. I do color matching everyday by trade and it takes years to master if you want to do it quickly. I use 2 part epoxy based inks for my trade so I use these on my restorations. These are very expensive inks some as much as $300.00 a quart or more but they are extremely durable and do not need to be covered with a clear coat or mylar to protect it, even in high wear areas. And they mix really good for getting the right shades of color. Unfortunately due to the cost this is not feasible for the average person to use.
Sometimes it's easier to recolor a whole area rather than try to match just a spot of it. I reccomend this when you can.
Also very important! The inks I use don't change color when they dry but some of the other paints in craft stores do...This makes color matching a tedious task because you have to wait for your color to dry before you know if it's correct.
One more thing....Take your time. Rushing a restoration is asking for trouble.