You have to weigh up several factors into this discussion, none of them we really know.
1) How much more money does Sony make on average for a PSP-Go than on a PSP (including software sales)
2) How much money did it cost to develop the PSP-Go
3) How much money could Sony have made from development with the resources used to develop the PSP-Go if used on other projects
4) How much have the Sony brans of PSP and Playstation been decreased or increased in value by the PSP-Go
Personally I think a relaunch of the PSP could have been much more successful than that of the PSP-Go.