In the wet helmets and motorcycle gear are the way to go. Rain should not increase the likelihood of any mechanical issues. I have driven my M3W over 30,000 miles some in monsoon like rain, whilst I wouldn't call it pleasurable it is doable.
If you do drive it in heavy rain, remove the seat squabs afterwards to dry as they will have likely got wet both top and bottom, also extend the seatbelts and hook over wing mirrors to dry.
