This isn't the first MiB/Tenchi crossover I've seen, and of course the 
other one went pretty much the same.  The problem is...yeah this is 
pretty much a vacation for the two MiBs.  Nothing much has happened
or is going to happen as things stand.  What you could use is a bad guy.
Perhaps someone else shows up wanting to capture Ryoko or the MiB get
to go up against Kagato.  Something.  

Oh, and I hardly thing with that much spaceship activity that the MiB
would need Washu to tell them something was going on.