This paper evaluates the impact of augmentation strategies for maintaining facial similarity in Stable Diffusion personalization for generating professional-quality portraits from amateur photographs. For two personalization methods, DreamBooth and InstantID, we compare and analyze the conventional augmentation (left-right flipping, cropping, and color adjustment) with the generative augmentation using synthetic images of InstantID. We quantitatively evaluate facial similarity using SDXL and a novel FaceNet-based FaceDistance metric. The experimental results show that the conventional augmentation can produce artifacts that hinder the identification of people, whereas InstantID improves fidelity when used in a balanced manner with real images to avoid overfitting. A user study with 97 participants confirms the difference between the preference for the refined appearance of InstantID and the accurate identification of people of DreamBooth. The results of this study provide insights into effective augmentation strategies for personalized text-to-image generation.