Plenty could be done with Linux on GP32.
In it's most basic form, you could use it to manage data on the SMC, removing the need for a program like COMI. You could edit and read text files with it, you could possibly connect to an FTP server (via serial cable) and download programs without the PC Link software.
If the wireless multiplayer adaptor can be accessed, there could be even more functions added. It may be possible to connect to a BlueTooth enabled home network to transfer files, play MP3's stored on a centeral computer, analyze network traffic, etc.
If Linux could be ported, without loosing too much functionality, it could easily revitalize the entire GP32 scene. It would be, without a doubt, the single most important development on the GP32 to date.
As for the question of "why try and port it", the same could be said for anything. Why emulate the NES? Why make a DOOM port? Questions like that would have us all still playing "DyHard".
A big part of the Linux community has been simply seeing what is can be ported to. That's why there is a watch that runs Linux...