Indeed we are not created to worship Allah as an ending target, worshiping is only a mean, a path toward our ending goal. Note the third group in the following quotation, they are the only ones who have understood what is the Right correctly:
قال اميرالمؤمنين عليه السلام: إنّقوماً عبدوا الله رغبةً فتلك عبادة التّجار وإنّ قوماً عبدوا الله رهْبةً فتلك عبادة العبيد وإنّ قوْماً عبدوا الله شُكراً فتلك عبادة الأحرار --نهج البلاغه/ حكمت ۲۳۷
Imam Ali --peace be upon him-- has stated: [Among those who worship Allah] one group worships Allah in hope [of profit], such is the worship of traders; and another group worships Allah out of fear [from His Wrath], such is the worship of slaves; and yet another group of people worships Allah out of gratitude, such is the worship of free noble men. [Nahj al-Balaghah, short saying #237]
Also according to Islamic theology the Determinism holds, God never chooses among the choices, there is only one choice possible (according to the rules God has set up in this universe) and that's what God does in this universe. That worshiping Allah is the way for a human to spiritualy grow and evolve is not a choice of God among the choices but the very natural and obvious way. He is the only Haq (حق) and we are as much Haq as we can get closer to the main source and that's what worshiping does. There are a lot that one can say in response to your question but I hope this much may suffice as a starting point for you to further think around the issue.
Godspeed.
Update. About your "update 2" if you can read Persian a detailed Philosophical answer is given here and here. However let me remark some points here:
(1) Everyone has a goal for doing something. We usually do something to improve and evolve in one way or another, in the favor of fulfilling our needs, but obviously God never changes, He is The Perfect and Needless. The goal of Allah for doing anything (creation) is not out from Him (ذاته) and that's the mercifulness of Allah, the Merciful. You can find it in the verse below:
وَلَوْ شَاءَ رَبُّكَ لَجَعَلَ النَّاسَ أُمَّةً وَاحِدَةً ۖ وَلَا يَزَالُونَ مُخْتَلِفِينَ / إِلَّا مَن رَّحِمَ رَبُّكَ ۚ وَلِذَٰلِكَ خَلَقَهُمْ ۗ وَتَمَّتْ كَلِمَةُ رَبِّكَ لَأَمْلَأَنَّ جَهَنَّمَ مِنَ الْجِنَّةِ وَالنَّاسِ أَجْمَعِينَ
And if your Lord had willed, He could have made mankind one community; but they will not cease to differ. / Except whom your Lord has given mercy, and for that He created them. But the word of your Lord is to be fulfilled that, "I will surely fill Hell with jinn and men all together." [11:118,119]
the true reason for why Allah has created any creature is to give it a mercy.
(2) the other point is the reason why His mercy reaches us through Worshiping Him. This has been somewhat discussed above and has been addressed in several Ahadeeth, but I guess this much may be suffice.