I think they could work very well depending on what end result you're looking for. You could use them to light specific areas of the marquee brighter or have lights flashing behind one of the graphics. I've seen redemption games that use LOTS of blinking lights behind a graphic effectively. I'm guessing they're done with 12V bulbs, but the christmas tree lights could get a similar effect. If you made a nice "grid" of the lights, I'm sure you could get a pretty consistant light behind the marquee. This is one of those nice things to try that while time-consuming, is pretty cheap.
While the christmas tree lights are an interesting option, I'm guessing working out the fluorescent would be the easiest and most authentic option. For a non-arcade related project I recently bought white plastic panels that are supposed to cover lights in a drop ceiling. They were only about $6 for a panel that was about 2-foot by 3-foot. It was very easy to cut to size. I bought mine at Home Depot but I'm sure any UK DIY center would have something similar.
The only other issue I might see is maintenance. If one of the lights goes out on those strings, it could be quite difficult to track down the bad bulb if the string is snaked around and balled up.
Does anyone know if anyone has ever tried "rope lights?" They're a string of LEDs in a plastic tubing. The LEDs would have a much longer life and generate less heat as well. Of course I'd probably buy at least one extra just in case it does ever go out. Might be worth trying.