You don’t need any additional passport if your current one is already allowing you good visa-free travel.
In terms of taxes, with the exception of the U.S. one, all passports are the same, as taxation is based on residence, not on
citizenship. However, this might change in the future for EU and UK citizens, so be careful and plan ahead.
If you can get a passport through residence, it doesn’t hurt and doesn’t cost you anything. Paraguay gives such opportunity, so I plan to eventually become (also) Paraguayan.