Should I upgrade or stick with my cheap uke?

I bought a cheap Mahalo U30G about a week ago because I wanted to give it a shot, it was cheap enough that if I didn't care for it I wouldn't really have spent any significant money on it anyway.

Well, I'm absolutely loving it. If my fingers hadn't become sore I would probably still be strumming away on it. So, I'm considering upgrading a little bit already to something that isn't necessarily expensive but that feels, sounds and looks a tad more like a real instrument.

You guys being the experts, is it worth it? I was thinking a soprano for somewhere around $120 - $150 (maaaybe a bit more, if there is a good reason for it). Thing is, I like having the real thing, and I'm worried I'll get bored with the plastic look and dodgy quality of the one I have and just stop playing, and I already have fantasies of playing songs for the children in the library (makes me happy just thinking about it).

So, should I? An suggestions would be greatly appreciated. :)