Are orthotics recommended for any foot instability or only if symptomatic? should they be used regardless to help prevent problems later on?

yes and yes: For the majority of us who spend most of our time on flat and hard floor surfaces, gain weight and loose flexibility with age - orthotics are indicated - as accommodative of functional corrective therapy options helping feet and general posture.

Orthotics: Can only help and not hurt. They can correct the most minor bio mechanical problem that they can prevent injury of deformity from developing.

Orthotics: When you say 'any ' that's a large category especially if you mean the type that lie in your shoes. They help a ton of biomechanical conditions. And can help prevent bunion formation , hammertoes , etc in later life. So , a long winded yes.