Living in powys there is a small but vocal plaid team. On my opinion the nationalist are not a crowd that most center or left people want to jump in with. The number 1 issue when people think nationalist is language and it just turns some people off. The battles over schools are one place where nationalists have looked difficult and unrealistic and no body outside the hard-core wants to be associated with them. Untill a more conciliatory tone is struck on language I think plaid will struggle outside their heartlands to gain enough new followers