The answer to your question is “it depends.” As you correctly note, the Torah and Rabbinic literature are full of examples of the rewards we will reap if we follow God’s commandments. Indeed, the notion of s’char va-onesh (reward and punishment for one’s deeds) is one of the tenets of Jewish faith. However, an attitude of “what’s in it for me” runs the risk of ignoring the fact that we are also held accountable for our sins and transgressions. We are bound to follow the entirety of the Torah – all 613 commandments – even if they are difficult and not necessarily enjoyable. The Gemara tells us that if a non-Jew is willing to convert to Judaism and accept upon him or herself “all of the commandments with the exception of one” we do not accept them as a convert. Judaism and Jewish practice is a commitment to the complete system of mitzvoth as written in the Torah and elaborated by the Rabbis.
There is nothing I do for which I know all the reasons I may do it. That means that even when I may be engaged in what appears to be completely altruistic behavior, it likely will include at least a touch of the pragmatic, an element of what's in this for me. And while I would love to imagine I'm free from the "taint" of reward, there is a part of most of us that seems unable fully to eliminate a certain (forgive me) Santa Claus view of deity and our concern for any divine naughty or nice list. Curiously, the famous song does end with a coda on point for this discussion. "So be good for goodness sake," in addition to being the only honest line in the song, implies that the reward for our good conduct – unlike the presents/bribes or punishments the song describes – is principally, were it only so, our growth in self and soul. But religion in general and Judaism in particular are not only for those who live exclusively in the rarefied heights of pure motives. No matter our age or stage, what's in it for me will likely intrude, at least occasionally. No doubt that is why, especially from a perspective that includes personal autonomy in decision-making, the tradition's reminder seems of the moment. Mitoch shelo lishma ba lishma. It may be translated or interpreted as "doing something good for the ‘wrong or ulterior’ motive may eventually lead to doing it for the right reason” (literally, for its own sake). Similarly, the Jewish people's response at Mount Sinai, na’aseh v’nishma (we shall do and we shall hear or understand). Or as Nike urges, "Just do it."