occasionally I am experiencing a front end shimmy that feels like a slipped belt

Sounds like a brake rotor out of parallel. Depending on rotor thickness it can be machined to true it up. Not a real danger but it is irritating and may get worse in time.

Try having rotors "turned" to with in specs. Or replace with new ones. Although not a big safety issue,it does cause unneeded stresses on other parts (shimmy, vibrations etc.) Have the steering parts looked over as well, for any signs or worn out parts.