Do intentions of seeking appreciation or good treatment or winning someone over interfere with the intention of loving to read the Quran and reciting it aloud, in terms of their effect on the reward for reading the Quran, and does this fall under the category of showing off?

Concealing righteous deeds is better than publicizing them, unless there is a strong overriding benefit, such as being further removed from ostentation (riya') and self-admiration (ujb). If you fear ostentation, then it is better not to recite aloud, in order to preserve the reward and seek perfect recompense. If you conceal your recitation out of fear of ostentation, you are combining two benefits and are not abandoning worship; rather, you are concealing it seeking safety. Reciting the Quran and vocalizing it to gain a worldly عرض (benefit/display) contradicts sincerity. Therefore, you must be sincere to your Lord, the Almighty, and seek nothing but His countenance, glory be to Him, through your actions. If you recite in the presence of people or are an imam and beautify your voice, your intention should be for people to benefit from the recitation, not for them to admire your voice and praise you; for this is blameworthy ostentation.