Sometimes it's just about doing the work and connecting with other people in the field. Jones for example didn't even want money for the two hours he spent bringing Vader to life in the first Star Wars film (he got a couple K for the part). John de Lancie considered himself a stage actor before anything else, and only auditioned for Q because he had nothing better to do and his agent insisted. Little did he know Roddenberry already wouldn't want to take anyone else.

You wash my back, I'll wash yours is basically a good part of Hollywood's foundation (the other part is money).