However, they also make fine targets, large ones at that. Yes, smaller carriers make equally opportune targets, yet they are not as costly to lose as a nuclear carrier and it's 5000 men.
Furthermore, why replace when you can renovate, for instance, USS Kitty Hawk and USS Constellation could be improved and prove suitable for further service, yet instead they sit as storage.
Each smaller carrier will require almost as many rank-and-file to operate as one large one.
They will be far less effective at flight ops- they are slower to launch strikes, slower on turnaround and unable to both launch and recover at the same time.
In short- it will be MORE EXPENSIVE to operate several smaller carriers than it is to operate one larger one... not to mention the increased expense of providing more escorts.
And, as has been pointed out- you can't renovate forever. Most of our carriers are >25 years old; that's old, even for a ship.
We have already unnecessarily weakened ourselves by accepting the myth of 'smaller numbers, greater technology.' Reducing numbers or capabilities of what we have now would be disastrous.