Wales is losing a possible £800m a year which could revitalise the health service, improve roads and transform the valleys, Plaid Cymru has claimed.
Plaid Cymru's Dai Lloyd says the NHS needs more beds
The party said "outdated and unfair" rules used by the Westminster government ignored the needs of Wales.
Plaid renewed its call for the abolition of the "Barnett formula", which was adopted by the Labour government in the 1970s, but has been disowned by its creator, the former minister Lord Barnett.
Meanwhile, the Conservatives claimed Cardiff's potential was being overlooked by the Welsh Assembly Government, and the Liberal Democrat blamed the Labour-run Cardiff County Council for the dirty state of the capital.
Plaid Cymru candidate for Carmarthen East and Dinefwr Rhodri Glyn Thomas said his party would negotiate with the UK government to scrap the Barnett formula.
About half of Welsh public spending was calculated under the system, but it was based on population, instead of the needs of Wales.
Plaid Cymru said another £3.2bn over four years of the next assembly government could deliver 2,000 extra nurses, 100 more doctors, and an improved roads network to link up Wales.
We believe Cardiff has been badly let down
Conservative Jonathan Morgan
Dai Lloyd, Plaid's health spokesman, said the NHS did not need further restructuring but more beds.
Mr Thomas denied that Plaid would be less able than Welsh Labour to persuade Labour in Westminster of the case for change.
"We are talking about the needs of the people of Wales, and the job of the government of Wales is to represent the people," he said. "We will take that argument to the treasury."
The Conservatives concentrated on Cardiff, which they said should be developed as a world class capital worthy of the whole of Wales.
The Tory "flagship" proposals for Cardiff included setting up a Welsh national art gallery at City Hall, developing a modern road to Cardiff International Airport, and supporting a new children's hospital.
Liberal Democrats say rubbish is a major problem in Cardiff
Cardiff North candidate Jonathan Morgan blamed three cabinet ministers from Cardiff - Labour's Rhodri Morgan and Sue Essex, and Liberal Democrat Jenny Randerson - for failing to do enough for the city.
"We believe that the assembly should be doing much more to promote Cardiff," said Mr Morgan. "We believe Cardiff has been badly let down."
Mr Morgan said the assembly government had given lacklustre support to Cardiff's bid to be 2008 European city of culture, and failed to sort out the capital's budget settlement which led to a "huge rise" in council tax.
The Lib Dems were also campaigning in Cardiff. Jenny Randerson, the candidate for Cardiff Central, gave the "Russell Goodway garbage award" to Glynrhondda Street in Cathays.
The "award" is named after Cardiff's council leader, and Ms Randerson said it was recognition of the growing litter problem across the city.
The Lib Dems said the council should supply residents with large wheelie bins and increase garbage collections to two or three times a week, and sweep pavements twice a week.