Data augmentation (DA) using large language models (LLMs) is a cost-effective method for generating synthetic data, particularly for tasks with scarce datasets. However, its potential remains largely underexplored, both in terms of augmentation configuration and evaluation of synthetic data. This paper investigates LLM-based synthetic data generation for irony and sarcasm, two subjective and context-dependent forms of figurative language. We propose a multi-aspect evaluation framework assessing synthetic data’s utility-plausibility and extrinsic-intrinsic dimensions through four aspects: predictive performance, sample diversity, linguistic properties, and human judgment. Our findings indicate that other aspects of evaluation, like diversity and linguistic features, do not necessarily correlate with an increase in predictive performance, underscoring the importance of multi-faceted evaluation. This work highlights the potential of LLM-based DA for irony and sarcasm detection, offering insights into the linguistic competence of LLMs. As synthetic data becomes increasingly prevalent, our framework offers a broadly applicable and crucial evaluation method, particularly for linguistically complex tasks.