Swapping spindles yearly would be good idea for as you say insurance. Through the years most LCOs learn what weak spots their machinery has so when it goes out they can already have the part on hand. I had an Exmark Lazer Z years ago when they were a cutting edge brand at a budget price. Since then I have heard about some of the complaints folks have had with decks. They are still a very good brand but no longer any price advantage that I have witnessed. I am a Hustler guy now and also at the stage I am in, price is not really a factor. I will ride the best machine I can find. Mind you, I am a small operator with a very small fleet.
1985 Jeep J20
2011 Hustler Super Z