Why do Nusahos Ari, Sefard, Edot HaMizrah, and Ashkenaz of Eretz Yisrael repeat the order of the kitores (incense offering) at the end of Shaharis every day and why does Nusah Ashkenaz of Hutz LaAretz repeat it on Shabbasos and Yamim Tovim?
I can't answer for the minhag of Ashkenazim Hutz L'Aretz. However, the reason that it is brought at the end of Davening "again" has deep Kabbalistic significance. According the Arizal and the RaShaSh, when we say pitum Ketoret and Korbanot at the beginning of davening, it is to draw down spiritual light in order to be able to lift our selves(and the world around us ect.) to the next spritual level(from Asiyah to Yetzirah). At the end of davening however it is to draw down spiritual sustenance to ourselves(and the world around us) for the rest of the day(from Yetzira to Asiyah). See the siddur HaRaShaSh and Sha'ar HaKavvnot Drushei Tefillat Shaharit Drush 3 starting on 12b.
As far as Ashkenazim Hutz L'Aretz... I can only hazard a guess. However siddur HaPardes(which is a Kabbalistic siddur arranged by one of the students of the Gra) does do it.
If I recall from Rabbi Artscroll, the initial ketores (before psukei d'zimra) is part of the recitation of the other sacrifices, which our prayers fill in for.
The additional reciting the order of ketores is auspicious for financial health, just as in the Temple, the Cohen offering it would be blessed with wealth.
A Chutz-la'aretz Ashkenazi like me, however, tends to be in a rush on weekdays. If someone omitted an ingredient from the ketores, that could incur Heavenly death; so it's considered very, very dangerous to recite the paragraph if you might skip words. Hence, save it for the more leisurely days.