While there's close to 70 per cent carpark occupancy at peak times, council officers said there was capacity to allow for longer parking.
The plan submitted to councillors also makes minor tweaks to other parking rules including St Hill St, the city's airport, disabled parking outside of the main town centre and parking exemptions.
It's the bylaw which allows council to enforce these rules.
The changes are closely allied to the regeneration strategy for the city centre which wants to encourage more pedestrian activity and longer stays for visitors which in turns promotes extra economic activity.
Council planners argue that having people stay longer in the CBD is one way to generate more spending.
And there are minors changes suggested for parking spaces along St Hill St, between Guyton St and Ingestre St, recognising the change of activities on this stretch of the inner city roadway, especially since the Ministry of Social Development office opened.
The management plan also looks to bring parking activity at the airport within the bylaw. At the moment it sits outside which means parking rules cannot be enforced.
As well as a passenger drop-off zone, the plan looks at 60 minute parking close to the terminal along with secure long-term paid parking.
Disabled parks, super gold card parking allowances and tradesmen's parking options would remain.
And the new rules will cover the stopping, standing or parking of vehicles in areas that could adversely affect the safe or efficient use Whanganui streets.
But while the changes will be welcomed by some, there will be a financial impact.
Based on council;s 2017-18 budget, it's estimated that removing or changing the charging regime in the central city will mean a loss from income and fines of about $340,000.
The report said while operating costs will drop, the annual rates requirement will lift from $42,000 (2017-18) to between $190,000 and $260,000.
Income from parking charges and fines returned $111,000 to rates in the last financial year.
"A combination of parking meters and sensor parking is expected to increase the collection of tariffs through greater self-enforcement and more efficient monitoring (by council staff)," the report said.
If council decides to retain parking charges then provision would have to be made to renew the meters within the next five years, expected to cost more than $857,000.