"More despoiled" means something that has been robbed, pillaged, or ruined to a great extent. The antonyms of "more despoiled" would be "undamaged," "untouched," "guarded," and "protected."
If we talk about a forest, an undamaged forest is one that has not been deforested or burnt down. A protected forest is one that has been safeguarded from encroachment or illegal logging. Likewise, an untouched beach is one that has not been littered or polluted, while a guarded beach is one that has security patrols to prevent theft or crime.
In short, the antonyms of "more despoiled" are words that signify preservation, conservation, and protection, rather than exploitation, degradation, and destruction.