I've got what I believe to be one of the most useful passports in the world (UK) but would like to have another non-European passport to allow easy travel to say OZ/NZ but I wouldn't say its essential to have that passport as you can get by with visa's etc (although its easier if you are given a passport of course, lol).
A lot of countries don't allow dual citizenship though so if it came to living in another country and asking me to give up my passport for theirs I don't think there would be a country I would do that for - mostly for the (apparent) safety and security provided for me in old age. I know others have better services but I'd rather be old and sick in a country I can complain about justifiably! :)
If you could collect them from just living in the country for X number of years and build up a collection I'd probably try to pick one for Asia / S America and Australia so I could travel among the lot throughout my life.
