All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
The rewards stated in these ahaadeeth are earned each time the person recites the Thikr (expression of remembrance of Allah) in reference. Al-Mubaarakfoori wrote, “It means that each time a palm tree is planted for him.” [Mirqaat Al-Mafaateeh]
Ibn ‘Uthaymeen wrote, “This means that each time the person says it, a tree is planted for him in Paradise.” [Sharh Riyaadh As-Saaliheen]
This is also evidenced by the hadeeth to which you have referred in the question. It has been narrated on the authority of Mu‘aath ibn Anas Al-Juhani, may Allah be pleased with him, that the Prophet, sallallahu ‘alayhi wa sallam, said, “Whoever recites Soorah Al-Ikhlaas (no. 112) ten times, Allah will build a palace for him in Paradise.” ‘Umar ibn Al-Khattaab remarked, “Then, I will recite it many times, O Messenger of Allah.” The Prophet, sallallahu ‘alayhi wa sallam, said, “Allah is The Most generous and has the best rewards.” [Ahmad - Al-Albaani graded it hasan (good)]
Had this not been the case, then the one who says it once and the one who says it more than that would be equal in reward!
We should not find this strange in the slightest; verily, Allah, The Exalted, is The Most Generous. His generosity is evidenced by the authentic hadeeth narrated about the man who will be in the lowest rank of Paradise (i.e. the last of the people of Hellfire who will be brought forth from it and admitted to Paradise; he will be the last of the people of Paradise to enter it). It was authentically reported that Allah, The Exalted, shall say to that man, “Go and enter Paradise, for you will have the like of the world and ten times more.” [Al-Bukhari and Muslim]
There are many good deeds that the Muslim can do to elevate his status in Paradise, such as building mosques; ‘Uthmaan ibn ‘Affaan, may Allah be pleased with him, narrated that the Prophet, sallallahu ‘alayhi wa sallam, said, “Whoever builds a mosque for Allah, He will build a house for him in Paradise.” [Al-Bukhari and Muslim]
Another such good deed is observing the regular voluntary prayers. Umm Habeebah, may Allah be pleased with her, reported that the Prophet, sallallahu ‘alayhi wa sallam, said, “If any Muslim prays twelve Rak‘ahs (units of prayer) (regular voluntary prayers) every day, over and above the obligatory ones, for the sake of Allah, Allah will build him a house in Paradise.” [Muslim]
It has been reported that the martyr is rewarded with seventy-two Hoori wives in Paradise. The Prophet, sallallahu ‘alayhi wa sallam, said, “There are six things with Allah for the martyr ... he is married to seventy-two wives from the Hoor of Paradise.” [Ahmad and At-Tirmithi]
We did not find any hadeeth about the good deeds that help the person have a greater number of servants in Paradise.
Allah knows best.