Hi Chris,

The E30 was designed to run on whatever fuel is available. In most cases the 'regular' grade of fuel is perfectly adequate. However on older cars that no longer run to spec, you may find that the lower grades of fuel cause engine knock or detonation. If that is the case then move up to the next grade.
If the car is stock and has had nothing done; performance wise; it should not need premium grades of fuel.

The only E30 that requires premium fuel is the M3 and it has a switch on the ECU if you are forced to use 'regular' grade fuel.

Don't get sucked into the myths about premium fuels giving higher performance or more hp; it just isn't do. Premium fuels have all the same detergents and cleaners as the regular fuel. They differ only in the antiknock ingredients required in high compression engines which typically run aggressively advanced ignition timing. All that the premium fuel does is keep the combustion temperatures down enough to prevent knock in those engines.

If you don't need it, don't use it...costs more money and adds additional polutants to the environment.

Hope this helps