I got 3 Map Pieces (Map piece 1, 3 and 5), and I was wondering if it's worth it to try to complete

If it's the Uncharted Land Map, it's worth it doing once in order to get access to a hidden part of the map (Omen Islands). If it's the regular Treasure Map, it's not really worth it in regards to the rewards you'll get in return, but you can collect achievements and forum titles with them, if you open several (up to 100 for the last achievement).

Nah, it's the regular ones. Thank you o/

completing the regular treasure map is a requirement for access to the blue building, so if that's something you're interested in, you might want to complete one for that purpose. (the blue building just has some quests, special items, and the ability to create a bumbus.)

Every year or so some users complain that the maps are "not worth it" and ups the reward, as if somehow this will compel everyone else besides them to sell their own pieces for less than market value.

You could hang onto your pieces until they next do this as a long-term investment in the obscurity of knowledge of economics? Me, I like Achievements but am not interested in seeing what the next new weird official intervention is, so I would do each kind of map once and sell the rest.

Completing 1 map gains entry to blue building along with other achievements

thanks