I always carry at least two spare pumps all the time, which has just accumulated over time. Of course the pump that you are showing is rated a lot more than most of the pumps that our mid size TTs use from the factory. I do this because I do remote camping a lot more than I do fancy campgrounds in populated areas. I also rarely use city type water hookups, even when I am at a campsite. Its just a habit that i got into by not trusting the crimped type fittings , even with pressure regulators. I don't want to have a leak and constantly flood the camper if i happen to not be inside and notice it.
But in my case its the head or even just the pressure switches that goes out, while the motors are just fine, as long as you have not let it run for hours and gotten them too hot. But its rare that this happens. But for most of the 3.0 and 3.5 gpm, the cost of buying parts to repair the heads and the cost for the entire unit is close to the same. the heads just unscrew and you install the new ones. There are some exceptions. But as long as your fittings are the same, by all means carrying an additional pump is like carrying a regular screw driver for me.