Should one gloat over cursing immodestly dressed women, or should one proclaim it? And does the curse include married women and others, given that the apparent meaning of the Hadith is to curse only married women?

It is not permissible to curse a specific Muslim or others. It is permissible to curse disbelievers in general. Whether to curse secretly or openly depends on what is dictated by the Sharia-compliant interest. The ruling of the Hadith is general and includes married women and others.