How useful are vitamin and trace element additions in E. coli culture medium?
Not sure that I have ever come across trace metals in recipes (I assume that you aren't referring to the Ca/Mg salts component of M9), but it is certainly the case that many K12 strains (e.g. C600, DH5&alpha;) require thiamine because they are thi mutants. This doesn't apply to BL21 since it is from a different lineage (it is a B strain). In a lab where several strains are being used it will always make sense to standardise on a universal recipe so that the medium available will suit all strains in use.

There is a useful list of E.coli genotypes here.