Restored, antique, rare or custom bikes will need special insurance for theft or damage, simply because most average motorcycle policies would not cover the replacement cost of the bike. If you have a unique cycle you may wish to consider additional insurance in the event of damage or theft of the bike.
Passenger liability is essential if you are planning on having anyone on the bike with you. Without this type of coverage you, as the driver, could be sued for any injuries to your passenger with regards to an accident with the motorcycle where you were found to be at fault.