That's a mind-opening statement. A lot of times we will try and convince people to perform mitzwoth because it is actually better for them. Either it leads to a healthier lifestyle, or it gives you a new perspective, or it will benefit you financially. From this halachah we can see a deeper level of mitzwah observance.
This isn't a new idea, it's clear from Pirkei Avoth: Don't serve HaShem like servants expecting a reward, serve Him like servants who expect no reward. (Or in the original: Serve Him like servants who serve in order to not receive a reward.) The Talmud also says it straight to the point: there are no rewards for mitzwoth in this world. (שכר מצוה בהאי עלמא ליכא)
Yet, how do we deal with this mindset, don't we enjoy the performance of the mitzwoth a lot, and shouldn't that be encouraged? The answer lies perhaps in Torah learning. We see that by Torah learning, one must always start out from a place of ulterior motives (shelo l'shmah) in order to get to Torah learing for the proper reasons. (l'shmah) Maybe it's the same by the mitzwoth, just no one told us, the reason we start to do the mitzwoth is for all the apparent ancillary benefits, but the reason we keep doing the mitzwoth is in order to serve HaSHem.
We can see this education happening almost automatically: When we discover mitzwoth, or a new mitzwah, we may perform it out of the simple pleasure of doing something new. Once we are already involved in the mitzwoth we arrive at all kinds of obstacles, times when perhaps it would be easier to ignore the mitzwoth or at least put them on hold. Yet, often we don't put them on hold, because when think about it, or even try it, it just doesn't feel right. Suddenly we're performing the mitzwah not because of how much we benefit from its performance, but rather because we feel it is necesary.
HaShem even built this system into the nature of the world. Our pleasure threshold naturally rises. Whatever got us very excited last week, is certainly less exciting now, and the more we are exposed to the exciting stimulus, the less exciting it becomes. We need to pursue new and more extreme forms of excitement. This is a truth of HaShem's creation that finds its expression in so many places, including our brain chemistry.
We might start to do something because it is exciting, but what will keep us doing that thing after the excitement wears off? Only our own discipline and effort.
There has to be a higher level, you are thinking right now. Life isn't just about how robotic and determined we are. There are endless passukim about enjoyment and pleasure. Two come to mind: והתענג על השם - enjoy HaShem (i'm pretty sure coke stole the idea from HaShem) and טעמו ורעו כי טוב השם - taste and see that HaShem is good. I think these two passukim clarify the issue pretty significantly. The mitzwoth aren't to be enjoyed for themselves. Rather, the relationship with HaShem that is brought about through the mitzwoth is what can and should be enjoyed.
If we were to enjoy the mitzwoth themselves then we would be possibly (heaven forbid) treading in the very murky waters of idolatry. What's to stop us from enjoying the mitzwoth for their own sake, thinking it is the mitzwoth that do good for us, and not (heaven forbid) HaShem who is good to us, because we keep His mitzwoth? Unfortunately we see this happening sometimes, when people want to take the mitzwah upon themselves for health or other reasons, but don't want to have anything to do with HaShem.
Still, I wonder about the various cases of Shehechiyanu, that seem to involve mainly a mitzwah. Like lulav or sukkah, or hannukah. In such a case it seems like the time component is the critical part, with HaShem's help we'll revisit this topic with a clearer understanding.