Agnew resigned for reasons unrelated to Watergate, unrelated to his service as VP.  
Pence has proven to be a willing, fawning, lying surrogate for Trump, and I think Pence's reputation will never recover.  However, even if there were grounds to remove him -- and I don't know that there are -- the result would be another VP nominated by Trump, or -- in the interim -- the advancement of Paul Ryan to second in line of succession.  None of this is good.