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.
update 2. Allah is not understandable to us, a big question mark that we have been forbidden to think about Him as is (not as influences our universe and His creatures), but that does not imply that Allah after all is a real question mark, He is fully understandable to Himself and other beings in His scale of existence (NOTE: it can be easily proved that the set of all such perfect beings is a singleton, that is only a unique God is existable, so only Himself understands Himself and no one else). Let me bring you an example. Consider a world of all possible ellipses. All the residents of such a world are closed curves. Now you try to make them understand a parabola, which is an infinite limit of a cylinder from the conic section point of view (when e tends to 1 from values less than unity). No matter how much you try to say a parabola is an open curve they cannot imagine, they will answer you "OK! We understand very big ellipses close at infinity but anyway you must agree that they close anyway, even if at infinity!" However, you that are sitting above the paper can write simply the equation of a parabola as simple as y=x^2. Roughly similarly we cannot understand God as He is like nothing else that we know or can know: "وَلَمْ يَكُن لَّهُ كُفُوًا أَحَدٌ" (And there is none like unto Him) [112:4] but He Himself know Himself as quite obvious. We cannot say anything about His side of view unless Himself describe it for us, as the holy prophet --peace be upon him-- told us in the Qadeer sermon (ref. here):
… وَ لا یَجِدُ أحَدٌ کَیفَ هُوَ مِن سِرٍّ وَ عَلانیةٍ، إلّا بِما دَلَّ عَزَّ وَ جَلَّ عَلی نَفسِه
… And no one would find out how He is from mentioning the secrets or the obvious symptoms, unless with His own guidances toward Himself.
We are told by Allah Himself that He is The Most Merciful, now the discussion would become two-fold: on one hand we must confess that Allah, the Needless, does not need to be a creator as He exists on His own and not dependent on His creatures (which are mostly evolveable in the course of time and He is unchangeable and just beyond the time and the space), and on the other hand we must admit that Allah, the unique in existence, is not comprised of parts, so that every reputation of Him must be with Him very intrinsically. Note that Allah is not even a unique being like a coin that has two sides, one side or aspect of Him being His very intrinsic being another being His Mercifulness, another being His Needlessness, and etc. However, we still have a chance to understand things better. Every deed has at least two aspects, one is the doer and the other is the action itself. If I do something I am doing that for a benefit of mine for example, I will be affected in one way or another at the end, but when Allah does something He will not be affected at all, He affects without being affected in any way: no need, no evolution toward a better qualification, no change at all. So that creation when is done by Allah affects only the creatures and the creator is far beyond the reach of any effect from His creatures, He is just beyond the universe of all His creatures, beyond the time and space, although not being outside of it as well. If you feel the more that you think the less you can understand that's because we are all ellipses and God is the in-understandable parabola (analogy to understand better not to be rude at Allah, Glory to Him). We are told in Hadeeth that insisting on understanding the in-understandable God would cause in denial of Him and thus, Kufr, so must be avoided, all that is said above is only to make the issue understandable as better than nothing. Neither He wants (likes) nor He needs to create us, He has just no personal interest in anything and nor even a single need to be satisfied, neither then need to create nor need to be known and worshiped, He creates only for the benefit of the created being as He is the Merciful, that's all, His deeds affect only the created object not the doer. Adhering anything to this sentence that introduces an influence of Allah on His created Universe affects Him in return is human-understandabl-ization of Allah and would definitely be accompanied by Kufr or Shirk. If then you ask if Allah has control on His power again you have indeed tried to make the God understandable to yourself, intuitionalize Him.
If your answer is not answered yet then I can only hope that someone else would answer you better.
