One of the standard arguments against the creation of new states has always been that it will increase the number of politicians. This has always been a hard argument to attack, not on the facts but on the prejudices embodied in the claim.
Back in the 1920s, the New State Movement responded with a double barreled argument.
Barrel one was that each person would still vote for the same number of people; state members, federal members plus whatever system of local government was in place. Whether the actual number of politicians increased depended upon the number of members in the New England parliament as compared to those in the NSW parliament representing the same area.
Barrel two was the actual cost per head to taxpayers of our system of representative government. This was quite low, an insignificant amount in the totality of Government spend. It would remain tiny even if the number of members was greatly increased.
Today, we have a further argument.
In both state and federal houses, the number of electors per member has greatly increased compared to the past. If you accept, not all do, that a key role of the MP is to represent his or her electorate, then the increased size of electorates makes it harder for the MP to actually represent that electorate. Yes, we have increased resources available to MPs meaning that costs have risen, but actual representation has dropped for most electors.
You can argue whether or not this is a bad thing. I think that it is. Regardless of that, it is hard to mount an objective argument against new states on the grounds of increased number of politicians.