Van Dijk will move to Anfield when the transfer window opens in January after the Reds agreed to pay what Southampton claim is a new world-record transfer for a defender.
Guardiola is familiar with the scrutiny that accompanies major outlays on members of the backline, City having parted with significant sums to recruit John Stones, Kyle Walker and Benjamin Mendy since the Catalan coach arrived at Etihad Stadium.
"It's about the guy, not the money," he said.
"I know that Liverpool took an amazing player. Van Dijk is an exceptional central defender.
"We will see in the future [if he was worth it]. Sometimes the cheaper players are more expensive than the expensive players. If he plays six, seven, eight years at a high, high level, it will be cheap. If he plays not good, it will be expensive.
"John Stones, when he came here, [people] said 'oh, it's too expensive'. Now, it's too cheap. [It] only depends on the value of what happens on the pitch."
While Van Dijk's transfer has dominated the recent headlines, and City's expensively assembled midfield and attack have earned plenty of plaudits this season, Guardiola took an opportunity to single out Nicolas Otamendi for special praise, describing the Argentine centre-back as a key component in the team's march to the top of table.
"We have a superman in the team, without Nico it would not be possible to do what we have done," he said.
"We speak about a lot of players. If I can point to a player who deserves a lot of respect for what we have done, it's Nico.
"He has been amazing. Even with pain in the knee, ankle, back, he always fights. One of the [toughest] competitors I've ever seen in my life. He was so important.
"I cannot imagine being in the situation we are in, in terms of the table, in terms of the way we have played, without him."