Ziyādat al-maʿnā means adding a relevant nuance or idea that strengthens the earlier expression. It does not mean indiscriminately attaching more adjectives. The addition should serve the rhetorical purpose.
For example, a later poet might depict a consequence of generosity that makes its praise more vivid. This would be a semantic enhancement, not merely a substitution of words.
Extra words that weaken coherence or distract from the intended point do not count as an expressive gain.