The Liberal Democrat leader criticised Labour's pledge card as "weak" and said Tory plans to cut taxes would damage public services.
" We are going to have transparent, modest and fair taxation "
On Thursday, he took his promise for "transparent, modest and fair taxation" to pay for quality schools and hospitals to Southampton, Plymouth, Cardiff and Nottingham.
And continuing his tour in Wales, he argued devolution had made nationalist parties irrelevant in general elections.
Mr Kennedy said voters knew "you can't get anything for nothing" and suggested the other parties were being dishonest over taxation.
Pledge card under fire
He said Labour's promises should not be believed because they'd failed to deliver on the pledge card of 1997.
Labour launched its pledge card on Wednesday making aspirational promises on the economy, education, health, crime and poverty.
But Mr Kennedy said: "If they can't honour those scale of pledges what credence can we give to much more aspirational commitments they are making this time."
Speaking in Plymouth, he said the Tories had not produced a "serious manifesto".
People were not suffering from the "collective amnesia" William Hague and Michael Portillo wished for, he argued.
They would remember successive fuel tax increases under Tory chancellors.
"This is a manifesto which is clearly written for a party which does not think it has a chance of winning," said Mr Kennedy.
He argued the Conservative plans were "largely uncosted".
'Honest on tax'
The Lib Dem leader promised his party would be honest about how better public services would be paid for.
"There is no point in politicians at this election going into some Dutch auction over income tax and somewhere being able to conjure out of mid-air better public services."
He added: "We are going to have transparent, modest and fair taxation to provide better local schools, local hospitals and improve the way this society of ours provides for pensioners."
On the Welsh leg of his trip, Mr Kennedy argued voters in general elections would see parties such as Plaid Cymru and the Scottish Nationalist Party as irrelevant.
"More of the issues that affect Wales can be resolved in Wales, therefore I don't see what logic there is in wasting votes for Plaid in terms of a Westminster election."