I'm glad you enjoy them! They're fun for me too, they just take a long time due to sheer volume.
I find it easier to be imaginative within constraints. So when someone asks me "What's the Cradle equivalent of a piano?" I tell myself that I have to give them a satisfying answer. I can't just say "There is none," or "It's a piano," unless there's a story reason to do so. I have to actually invent a Cradle piano.
Which is fun. It makes me consider avenues of the worlds that I hadn't considered.As for your trying to be imaginative, it's not like my systems are the most original magic systems ever designed. I just give myself permission to have fun with it.
I start with what general kind of magic I want the people to use. For Traveler's Gate, I started with the idea of an extradimensional mansion where you went for martial training. I knew I wanted the House to exist, so then I built a world where extradimensional training grounds were commonplace.
For Elder Empire, I started by knowing that I wanted a world where significant objects held automatic power through their significance. Excalibur wielded by King Arthur would have automatic power BECAUSE it was Excalibur and BECAUSE it was King Arthur's sword. Then I worked out from there.You can do that too. And there's nothing wrong with using principles from known magic systems; madra is basically just elemental mana.
My main weakness is that I throw in everything but the kitchen sink. Every idea I can think of goes in. There are more Territories than necessary, for instance. Too many Guilds. Reading, Awakening, Soulbound, etc. are more complicated than they need to be, and could probably be separated into two systems. Vital aura is essentially elemental energy, but by trying to integrate it into the madra system I accidentally made it muddy and unclear.
No approach is perfect, but I like mine because it's fun. My magic systems might be too unintuitive or complicated, but they're colorful and fun. That's my priority over a logical, fully hammered-out, and ultimately simpler system.Of course, the Holy Grail is a simple, intuitive system that nonetheless fires your imagination and can be used to create as many fun and colorful situations as you want. And toward that distant goal, we all strive.