Does the virtue of guiding a single person mentioned in the noble Hadith, "For Allah to guide a single man through you is better for you than red camels," apply only to bringing a non-Muslim into Islam, or does it also include bringing a misguided Muslim back to guidance?

The aforementioned hadith is applicable to the generality of this meaning. Allah's bounty is vast. This statement was made by the Prophet to Ali ibn Abi Talib when he handed him the banner on the Day of Khaybar. The lesson lies in the generality of the wording, not in the specificity of the cause. Other hadiths have been narrated encouraging people to invite others to good and highlighting the immense reward for the one who invites. Among these is the hadith from Abu Hurayrah in Sahih Muslim: "Whoever invites to guidance will have a reward similar to the rewards of those who follow him, without their rewards being diminished in the slightest..." Therefore, inviting one who neglects fasting or zakat to perform them, and guiding him, is better for the inviter than red camels.