When I worked on XEmacs, I acquired many systems and compilers and used them to test XEmacs. Quite aside from creating new ports that are actually useful to users, each successful port is a Quality Improvement exercise. Each new port typically finds new bugs. I recall one particularly insidious bug found only using the 64-bit Irix compiler.
So I'm a big fan of at least porting to many compilers. But the culture of JDK development is not quite right to reap maximal Quality benefits from this activity. Martin