Economy spokesman Adam Price told BBC Wales that health and education could be the main beneficiaries of the idea.
He said the money could "transform" health and social care through a new integrated service.
It could also boost education, where he said spending in primary schools was £600 less per pupil than in England.
"We're beginning our preparations for the programme of government we're going to be putting in front of the Welsh people in the 2021 election," said Mr Price.
"We'll be consulting on this key question of what we should do with those new income tax powers.
"We'll be the first political party in Wales openly exploring the idea of having a dedicated penny for health and social care, which actually invests in this transition to a new integrated health and social care service.
"Creating that additional capacity so that we can transform the level and quality of care is something we could do.
"We'll also be asking the same question about education as well.
"A dedicated penny increase in income tax. What could that do in terms of our schools?"
Mr Price added: "We know relatively speaking, when the last time we had comparative figures, £600 less per pupil in the primary sector in Wales compared to England.
"If we were to decide as a society we wanted to actually achieve world class quality of an education system, would there be an appetite out there for actually using the income tax powers that we have as a nation?"
On Friday, leader Leanne Wood told the conference that voting Plaid was the only way for people in Wales to "be in control" of their lives.
People in Wales could be asked to pay an extra 1p in the basic rate of income tax to boost public services, the Plaid Cymru conference will be told later.