Significant rates of amino acids racemization would no doubt be lethal to the cell. The Archaea are, as a group, more primative than are either the Bacteria or Eukaryotes. Although modern Archaea are not the ancestors of other modern organisms, they probably do resemble in many ways these ancestral life forms. In may be that they haven't changed much because of their thermophilic environment - evolutionary drift in genes is much more constrained in thermophiles than in mesophiles, because their macromolecules are less tolerant of minor perturbations that are allowed in molecules than function at lower temperatures. But the mismatch is a big problem for a thermophile because of the thermal destabilization it causes, making it much less likely that a compensatory change will occur before the decrease in fitness leads to extinction.
Halophiles are directly responsible for decomposition of salted meats.
Conceptually, at least, RNA secondary structures are likely to slow their evolutionary rate as the growth temperature of the organism increases.