In the past two years, since the launch of the global phenomenon Pokémon Go, the value of the cards jumped as many people were hit with a dose of nostalgia, Maggs said.
Sales for the little pieces of cardboard are frequent, with Trade Me reporting around 1300 sales a month.
It comes on the heels of a landmark sale in the United States earlier this month in which a pack of "Pokémon 1999 1st edition limited print base set unopened booster box" sold for NZ$87,000.
The trading card game was a schoolyard phenomenon in the mid-nineties and early 2000s, however most Kiwis from that generation binned or put them in storage with other pieces of childhood memorabilia, Maggs said.
Some popular cards have doubled in value since the introduction of Pokémon Go, Maggs said.
"A classic Charizard would have been $50 to $70 bucks, then it moved to $100 to $150. It inflated things a little bit.
"For cardboard it's crazy."
Since the release of the mobile game, Maggs estimates he has sold about 5000 cards.
His best sale came a few months ago when he sold a mint Ho-Oh for $2200.
"I bought that for $180, when I got it from my friend it was in mint condition."
He advised Kiwis to look in their storage, there might be a few hundred dollars just waiting.
Pokémon, a billion-dollar company, is based on a Japanese cartoon which also spans dozens of video games and other merchandise.
Trade Me spokeswoman Millie Silvester agreed with Maggs, saying there was a resurgence for the cards when the Pokémon Go phone app was released in 2016.
"In the past month we've seen over 1700 searches for Pokémon cards on Trade Me and we typically see about 1300 sales every month."
Mercer chief investment officer Philip Houghton Brown said the majority of investments in Mercer were shares and bonds, and alternative investments probably accounted for 10 per cent.
Things such as art work and trading cards were more of a private investment that would be less than 1 per cent of investments.
"I have heard of people investing in collectables like cards, but it is a very specialist area."
In the past five years he had noticed a trend of traditional investors moving to alternative investments in a bid to diversify assets and reduce the impact of fluctuation.
"I think there has been a shift towards non-traditional assets in the past five to 10 years."
The rarest Pokémon card to go on sale, the "Pikachu Illustrator", of which there are only six in the world sold, for NZ$85,000 in 2016.