I was thinking about 3 runways with overlapping ends on shoreline, with central area of Minamitorishima dedicated for radar station and storage. The area is still enough, although the dense storage would be vulnerable by military standards and therefore costly to construct. Will need to import a lot of concrete and make a proper covered hangars and buried fuel tanks instead of blast isolation berms and above-ground fuel barrel arrays i observed on less cramped bases.
With area 1.5km2, Minamitorishima base can be ruined with about 300-500 tonnes of bombs - a quite substantial amount for Japanese capabilities of 1943
This is going to take a while. All for an exposed outpost that can't operate any serious number of airplanes. So a half-dozen B-25s could bombard Japan once a week. What happens when the battle fleet comes and shells the island? (The comments about rocket-assisted takeoffs are even more desperate attempts at justification.)
Supplying it will require convoys that will require not insubstantial escorts. As another poster put it:
To get to Marcus Island, you would have to go through Wake and the Marshalls among other places, and potentially be in range of Japanese bases in the Marianas. The Japanese may have lost the ability to go on the offensive after Midway, but they still had enough to make the US pay dearly defensively.
By 1944 when the Japanese had been ground down and the US had enough forces to launch major sustained offensive operations, there where more vital or worthwhile targets to choose from.
Granted, the attempt to take Minamitorishima can be the cause of a substantial naval battle, but more useful islands could be taken with the same amount of effort.