You do not need a second passport if you retire
You do not need a second passport if you retire and choose to work or live abroad. It is, though, highly recommended to get a residency, which, for example, in Nicaragua is a very easy thing to do. All you would need to do is pay $2 for the application, fill it out, get a couple of medical tests and then you are all set.
With this residency you wouldn't have to worry about migration problems, you will be able to come and go from the country and you are free to work in whatever way you may want. You will receive your retirement money as you would back in your home country.