Yonifalic, a few corrections. First, Maimonides accepted the Jewish law that determined that one is Jewish if one is born of a Jewish mother, or has converted to Judaism. One could commit all the transgressions in the Law and still be counted as a Jew, according to Maimonides Heretical Jews remained Jews, albeit heretics, whom other Jews are commanded to hate and even kill. As heretics, they should be excluded from the Jewish community. (See commentary to Mishnah Sanhedrin: Perek Helek). Nevertheless, they do not pass into the category of non-Jew. So it is not accurate, to say the least, to deny an ethnic component to being Jewish. But it is not a racial or metaphysical component.
Second, Maimonides says in his Mishneh Torah of a Jew who acts cruelly that his Jewish lineage is suspect. That seems to be his way of shaming Jews not to act cruelly, to say that they are not of Jewish lineage. But it is impossible to divide neatly the ethnic from the spiritual component of Jewish identity for Maimonides or for most Jewish thinkers.
Third, although Maimonides does not list the conquest or settlement of the Land of Israel as one of the 613 commandments (much to the consternation of religious Zionists), he clearly believes that the Land of Israel belongs exclusively to the Jewish people, and that when King Messiah comes, the Jews will have sovereignty in the land, and non-Jews will be able to stay provided they accept the Noahide laws and “dhimmi” status; they must go around humbly and deferential to Jews. He is one of the few Jewish legal authorities who discuss the laws of land of Israel in the messianic age, and, in fact, in any age where the Jews have the upper hand.
Fourth, Maimonides might think that Jewish traits pass from generation to generation, and he certainly believes in the superiority of Judaism, but he does not believe that Jews are in their essence different from non-Jews. Here he follows the philosophical, not the mystical tradition. (Halevy, who thinks otherwise, is influenced by certain Shiite conceptions.)
Fifth, Maimonides was deeply influenced, of course, by the intellectual and local environment of the twelfth century. He lived under four different khalifates in Spain, Morocco, and Egypt. And of course, he was deeply immersed in the Jewish and in the philosophical/scientific traditions. While we can certainly learn a great deal from him (I think), and while he can serve as a model and as a hero (he does for me), we all should remember that he is a person of the twelfth century. We’ve come a long way since then.