The other solar planets have few even theoretical benefits upon reaching them: The moon has He3, which could be used in nuclear fusion reactors...erm if we had any; Mars has uh, some water and probably some iron...

Billions are spent and we end up with precious little.

Far more important discoveries are beneath the sea. To get there there would also have to be technological breakthroughs, new equipment. Except that when something has been found it would be (comparatively) easy to utilise it.

If China wants a peak in the sky then great. If there's anything that's found which is of extreme use then the financial impetus is there to get back.
Else why not explore elsewhere rather than pincusion flags into anything that stays till long enough.