There is, in fact, something to be said for magic that doesn't make sense. It lets you tell wild tales that you couldn't reach any other way. It's fun. It is surprising, which is valuable in a glut of entertainment most of which is repetitive. This approach works best at small sizes. On a larger scale, you run into the problem of crossing your own trail, contradicting yourself, and thus annoying your readers. The bigger the story gets, the harder it becomes to maintain a whimsical mode of magic. It can be done, though. I find that it's one of those rare cases where it works best at the extremes: either your whole world is batshit, like Wonderland; or most of it is gritty with occasional flares of unexpected magic, like Middle Earth.
The value of making a magic system lies in structural integrity. The more you know about how something works, the more stable it will be as you write, and the more ideas it tends to inspire. You can make it very different from other people's systems. You can incorporate motifs from different cultures. Readers can learn about it as they go along. If you're just doing a short story, you don't need to build a whole system, just the parts you plan to use. But if you're doing a novel or any kind of series, it is worth your while to build the magic system first, because it'll save you time and make for a stronger story. This is much the same as with any worldbuilding.
That said, there is nothing wrong with making magical systems as a hobby. Some people like the challenge of building a ship in a bottle; others prefer to make model continents, languages, or magic systems. It's brainplay, and it's good for you. Don't let anyone tell you not to do a hobby you enjoy.
Conversely, there are no Fantasy Police. If someone doesn't like what you want to write, they don't have to read it or buy it. What you choose to write may influence your chance of selling your work -- but if you just want to share it with the world, you don't need anyone's approval for that now. Start a blog and slap up your wacky magic stuff.
Me, I like diversity ...
The Adventures of Aldornia and Zenobia, Gloryroad Crossing, the Inkseer, the Ocracies, the Odd Trio, Practical Magics, Seeing Hearts, and Sort Of Heroes all draw their inspiration from classic fantasy and roleplaying games. They include a variety of magic, some of it more systematic than others.
The Arc of Joan and the Steamsmith both belong to a setting where the science is based on alchemy. It has rigorous structure and follows the laws of scientific method, but the underlying framework of the universe is quite different from ours, so it reads a lot like magic. Steampunk can be fun that way.
The Bat Vampires and Frankenstein's Family are aspects of a gothic fluff setting that relies primarily on science, but some of what their science can do is out of reach for ours. Plus they have vampires with psychic senses and werewolves who can shapeshift. The structure comes in where I use real traits of bats and wolves to shape those cultures -- but I haven't gone into detail about how these werewolves shapeshift.
Clay of Life naturally uses Jewish magic, since it's about a golem. And that's one of the more structured systems around, but it's cleric magic, not wizard magic. Usually magic that you give from divine sources is faith-based and intuitive rather than systematic.
Fiorenza the Wisewoman includes just a dab of fairytale magic. So it doesn't have a rigorous system; if a thing can happen in fairytales, particularly Italian ones, then it's fair game here. But it only appears in a few places, not every day. The source material helps with congruity.
Fledgling Grace is all about spiritual magic, and one of the key points of the series is the sheer mystery of it. Quite often things happen and people don't know why. Sometimes they can figure it out in retrospect, but not always.
Kande's Quest has African magic. It's very different from European magic. It has spiritual and practical aspects, but a lot of it is ancestral, so the structure is a bit more like a family tree or even a family gathering.
Monster House is urban fantasy in which the "monster" types all have their own magic, and it's pretty different from each other. The Bogeyman can find bad children (or adults). The monsters under-the-bed and in-the-closet can warp space. Some aspects are borrowed from fairytales or legends, but most of it is based on the monster lore of children's folklore. It has a certain consistency of flavor, but very little in the way of rules.
One God's Story of Mid-Life Crisis is unusual in that the main character dispenses magic. Shaeth is currently involved in creating a new magic system for his new religion. He knew some applicable spells beforehand, has learned a few more from other sources, but he's having to build a lot of things from scratch.
The Origami Mage uses Asian themes to create a rather fussy pair of magic systems, which are quite closely related but are rivals. The structure isn't detailed but is heavily implied.
Path of the Paladins is another example of spiritual magic handed out by deities. It's fairly structured.
P.I.E. is urban fantasy with bits and pieces of magical content. Some of that may be systematic, but much appears only in glimpses so it may be more intuitive.
Polychrome Heroics includes both superpowers and sorcery. Some people with magic have a very systematic approach to it, while others are wholly intuitive. And then there's Antimatter, whose gifts lets him bend the laws of science, but only if he knows how they're supposed to work. That one isn't magic even though it functions similarly -- he just has Sysadmin access to the code of the universe.
What kind of magic do you like: systematic, whimsical, or all kinds?