Definitely don't disagree letters from Dr's shadowed wouldn't hurt but its far more impressive if you've actually did something for them- shadowing is more of a favor on their part. Even though they can gush about how enthusiastic you are about medicine, it doesn't shed light on your capabilities- again, unless if you did something like demonstrated strong work ethics under their supervision.. least that's what my advisor mentioned, otherwise you'd benefit far more by having a letter from an employee- my friend she used her "Build-a-bear" floor manager and at her interview, her interviewer was so impressed by what they had to say about her...in short,
since she always wanted to go into Peds, this letter really brought her application together and gave it focus. So don't forget people outside of the required science and humanities, who could vouch for your medical passions.
noted the 'knowing very little about your current application' wasn't trying to rip on your comment 2ndCareer, just adding to it