Thanks! I guess the whole kit is pretty cheap but I would think the bulbs would be even cheaper seeing as how the bi-pin adapter doesn't really wear out. I tried searching around in a bunch of old threads and it seemed like some people had varying degrees of success adapting other bulbs to the adapter but I didn't see anything concrete.
the adapter is plastic, sure you can use other g4 bulbs, but anything above few watts you are risking to melt the holder.
fivemega used to sell good holders that work in maglite and do not melt, but i'm not sure if they are still available.
me personally, i do not like new bulbs, i dropped my mag with new bulb, and it came out of the holder a bit on 1 side, had to remove the heads and push the bulb back, i like white star 1 bulbs better, i could not see any difference between WS1 and 2 beam wise.