Push to keep them as is. If rented, where will the money go, and who determines the rent? Presumably it will be used to reduce management fees? Reduction will probably be quite small, so will this outweigh the loss of the convenience of visitor spaces?
Presumably it is the people with 2 cars that are pushing for this? If so, approach the others with 1 car and get them to vote against.
I don't have much sympathy for people with 2 cars and one space - the made the decision to either buy/rent the apartment when they had 2 cars, or they got the second afterwards, either way they made a decision with eyes open.
Other residents who may have been (slightly) influenced by the availability of visitor parking when buying/renting shouldn't suffer.