i was quite disappointed with the way the upgrade system turned out, too many things had very little use not enough stuff to upgrade. you upgrade stuff for the sake of upgrading it
Those who stood by the upgrade system were more than likely pleased. It might have been especially pleasing to collect all of the collectibles, the Lizard Tails in particular. For them, the upgrade items/equipment proved more than useful, especially the variety of shields. If done right and at a gradual pace, it also served by giving
Skyward Sword the appeal of an RPG, which many fans liked, including myself.
The upgrade system seemed to be optional for the most part; those who were less dedicated to it, or rather, the collectibles, might have viewed it as such. It should not have been perceived as one of the game's shortcomings or a flaw, but instead, it should have been perceived as something you simply cared less about. If you didn't want to upgrade anything, you could have opted out. If you mistakenly picked something up, then, you made use of it or sold it; it shouldn't be difficult or frustrating at the slightest.
Anyway, yeah, the Lizard Tails can seem a bit useless when one considers the few upgradable items for which they are needed. However, when one considers the value and usefulness of said items, collecting the Lizard Tails are not so useless and more than worth finding and collecting. The aforesaid upgradable items include the Medium/Large Bomb Bags, and the powerful and effective Sacred Bow. Although, what is considered "valuable and useful" in this case are entirely subjective.