It's also worth noting that this unfortunately only seems to work if you have auto insurance - renter's or home insurance with motorcycle insurance alone doesn't net much of a discount.
That is true -- the only multi-product discount that companies usually offer on the bike is when you bundle the car.
i.e.
Bike + Car = Discount on Bike, getting close to 40% (and maybe a Discount on Car as well)
Bike + Life Ins = No Discount
Bike + Home/Condo/Tenant = No Discount
Bike + Bike = *Maybe* a discount on both bikes, getting close to 10%
Car + Car = Discount on both cars, getting close to 10%
Car + Life = Discount on Car, getting close to 10%
Car + Home/Condo/Tenant = Discount on Car and Home/Condo/Tenant, getting close to 10-20%.