i too have invested in suspension parts. i have never had a bike that i could not ride with the stock suspension, but found the improvements brought about to take the ride from acceptable to a real pleasure. bmw's were easy to do because of the front "paralever" suspension. with that, you did not have to pull springs from the forks, just changed one spring/shock unit. they took bikes that must have been sprung for 240 pounders and jolted on every bump to smooth riders with much more controlled handling. well worth the money in my personal opinion.
btw, the 2 guzzis i have had have come with factory suspensions that have worked well for me.