There is not much to improve. In the space I'm operating in, the software, as it is, can be considered more or less complete. I mean, I can always add features, but the core mechanics, the way it works, the way it delivers value and the value people expect from the software is more or less complete. There's not much to add that improves the perceived value for people in such a way that they'd be willing to pay more for it.
But the fundamental idea is right: There must be some additional thing that's good for people, that people want. There's also related products, added benefit, whatnot. I won't do Gold membership, but I might be able to sell different things that complete the offering for some people.
Compare this to Microsoft Office. Word is for writing stuff. It's more or less feature-complete. Sure, you could add some stuff, but most people are happy with how it is in its basic edition. So Microsoft offers also Excel and PowerPoint. They are for very similar people, they complete the offering, but they're totally different. A "Word Gold" wouldn't make any sense.
One more thing: Whatever I add and whatever pricing change I introduce comes at a cost. Introducing tiered-pricing (3 wiggles for 2 euros, 7 wiggles for 4 euros etc.) for example has benefits, but it also increases complexity and decision making. I'd do this for my next project, but for the current business, I'm also a bit stuck in the current userbase with decisions I made in the past.
I might offer my service in English as well next year. That's going to be an opportunity to experiment a little bit and a way to grow the business.