It is possable to make a unit to adjust the brightness of the leds, I wonder how many people would be interested in buying them if someone made a "plug and Play" type of dimmer with a trimpot you can turn to change the brightness?

It is posible to make led controllers and they do exist. Buckpuck are good examples but there are heaps of cheaper alternatives - look at Jaycar for a few and Deal Extreme for many examples. BUT you would need modifications to work in a pin.  Led brightness is regulated by current and that's how theses controllers work. To get them all the same current you want to pass the same current thru each led - this is done by arranging them in series.  Pins arrange GI in parallel, so you'd have to rejig the wiring, could be done - but I'm not sure it would be worth the effort unless you were rebuilding the pin.  If  you did you could get some interesting effects as some of these controllers will flash, dim etc and could be controlled programatically by the pin or features of teh gameplay. A sort of modern take on Blackout but with more bells and whistles.

For a variety of other (fairly boring to most!) reasons, the Cointaker or Ablaze leds would not be the best to use in this setuip either, so you want to look at making your own bases etc - it all starts to look a bit like too much work.