All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
There is no blame on you in giving used clothes in charity. Rather, this is considered recommended by some scholars if you buy new clothes.
Ibn Hajar Al-Haytami who is a Shaafi‘i scholar said: “It is a Sunnah that the one who buys new clothes gives the old ones in charity.” Then, he said: “Giving the old clothes in charity does not mean giving bad things; rather, one should give from that which he loves like the custom of giving charity from cash and not gold and silver.”
Ibn Al-Jawzi explained in detail the verse you mentioned in your question in his exegeses of the Quran. He said: “{The good [reward]} means one of four matters. First: Paradise. This was said by Ibn ‘Abbaas, Mujaahid, As-Suddi and others. Ibn Jareer said: 'Thus, the meaning is: You will not attain the benevolence of Allaah The Almighty to you which you demand with your obedience.' Second: piety. This was said by ‘Ataa’ and Muqaatil. Third: obedience. This was said by ‘Atiyyah. Fourth: the good with which the reward is deserved. This is the opinion of Abu Rawq.”
Al-Qaadhi Abu Ya‘laa said: “The negation is not intended to negate attaining the reward in principle but it negates its perfection (i.e. you will not attain the perfect reward).”
There are two opinions about the interpretation of {until you spend [in the way of Allaah] from that which you love.} First: that the slave spends from his money when he is healthy and close-fisted. This was narrated by Ibn ‘Umar from the Prophet, sallallaahu ‘alayhi wa sallam. Second: spending from dearly loved wealth. This opinion was said by Qataadah and Adh-Dhahhaak. There are three opinions about the intended meaning of spending; first: obligatory charity. This opinion was given by Ibn ‘Abbaas, Al-Hasan and Adh-Dhahhaak. Second: all the types of charities. This was said by Ibn ‘Umar . Third: whatever is spent for the sake of Allaah The Almighty whether charity or not.”
Therefore, there are different opinions of scholars regarding this verse. Spending from what one loves is a reason for reaching perfect and ultimate reward despite the debate about the intended meaning of spending. Giving used clothes in charity constitutes giving from one's dearly loved wealth as previously mentioned.