I would recommend sticking with v2 (unless there is something in v1 that v2 doesn't support) , but v1 has a boards/nested call to get all the boards in the community (the /boards call just returns the boards that are directly under the node you are in -- so /categories/id/[:categoryId]/boards would return just the boards that are directly under the given category).
Just curious (so we can improve upon v2), why do you want to use the v1 /boards call instead of using a v2 LiQL query? Is there a field or fields you need that is missing in v2 that v1 has?
-Doug