You can of course get rid of some blanks and such, and get
@1,2,4
{
requires:['Silk Road','Workshop']
gainPriority:(s,m)->['Workshop','Silk Road','Estate']
}
which is 94 chars (according to wc), and
@3:
{
requires:['Ironworks','Great Hall','Island']
gainPriority:(s,m)->["Ironworks","Great Hall","Island"]
}
which is 101chars.
Edit: A bit more compressed.
Edit2: (s,m) can also be obmitted, saving 5chars in each bot.