The sheer lack of textual commentary implies that this occurrence came about very soon after the formulation of the lex in the Republic, and the quotation from Gaius regarding recovery of fraudulently expunged debts does not seem to rest easily with the extant chapters (dealing which varying degrees of property damage).
In practice, this would mean that the aggrieved party would be entitled to monetary compensation equal to the diminution in value of the article which suffered damage.
Although Lex Aquilia applied only where damage was unlawfully caused, this requirement was satisfied wherever a person was neglectful or acting intentionally.
The Lex Aquilia could not force a rent object, slain slave, or herd animal to be replaced; it could only demand monetary compensation.
On this view then, the essential purpose of the Lex was to address Plebeian grievances against the Patrician elite during a politically tumultuous period by giving them a more equitable and comprehensive set of remedies.
On this line of reasoning, the Lex was enacted as a response to heavy inflation following the Second Punic War and was thus necessitated by a need to eschew an assessment of damages based on fixed penalties.