Anderson and Co Resource Management director Conrad Anderson said they should enhance the environment, but there would always be tension over differing uses of land.
"The reforms will take about 10 years to implement, during which I expect costs and complexity may get worse," Mr Anderson said.
Paterson Pitts principal Kurt Bowen said a transition period of 10 years sounded "terrible".
More work would be needed through that period from both planners for councils and development applicants, he said.
"I can’t see how the proposed legislation reform could possibly achieve the cost and time benefits that the Government is anticipating.
"I am sceptical that this reform will reduce costs, or simplify matters, or shorten consenting times.
"I would put $100 on the opposite happening without any hesitation at all."
The Government this week brought to Parliament two of three pieces of reform set to replace the Resource Management Act.
It introduced the Natural and Built Environment Bill and the Spatial Planning Bill, and the Climate Adaptation Bill is to come later.
Environment Minister David Parker has said the new system needs to be "faster, cheaper and better".
"The Government is delivering a new resource management system that will better protect the environment while cutting red tape, lowering costs and shortening the time it takes to approve new homes and key infrastructure projects."
Mr Anderson said watered-down local input into decision-making would be one disadvantage.
Planning documents would likely get much larger and would need to cover larger and more diverse areas.
He wondered if setting up 15 regional committees to lead local planning would put further pressure on local government, exacerbating loss of local decision-making.
However, wider geographical planning could be helpful for infrastructure.
Seeking enhanced environmental outcomes was a clear focus.
Mr Anderson said significant landscapes were likely to remain highly important, and may get additional protection.
However, a "local landscape" may not be seen as important by a regional committee.
Mr Bowen said many councils may not want to embrace the new legislation.
He expected councils would continue to interpret or apply their own views to consenting processes.
National-level reforms had historically not achieved improved efficiency, he said.
