Do they actually add an extra 300% game content given that they cost $188 compared to the main game's $60 price?

No they don't add anything with the exception of costumes. These are just mainly bonus items which you can farm in game and it is an extra way if you want to support the publisher/developer. I never purchase these items. I only just purchase the costumes. Now on Daybreak II also has a holo core voice pack DLC and BGM DLC which also adds some ingame content.

tldr; If you are only interested in costumes and holo core voice pack these should be the dlc's to purchase (when they go on sale obviously because they are very expensive). The others are just things which you can farm ingame:

https://www.gog.com/en/game/the_legend_of_heroes_trails_through_daybreak_ii_holo_core_voice_pack
https://www.gog.com/en/game/the_legend_of_heroes_trails_through_daybreak_ii_costume_pack
https://www.gog.com/en/game/the_legend_of_heroes_trails_through_daybreak_ii_accessory_pack
https://www.gog.com/en/game/the_legend_of_heroes_trails_through_daybreak_ii_bgm_pack