It depends I guess. Depends whether you like the feel of the cube and does your times improve with it or the cube sounds like the one for you. When I was a beginner I had a Guanlong and Aolong. Like Aysha, I couldn't tell the difference between the 2, but when I start to get better, I realise the Aolong is much much better than the Guanlong. That's when I started to think, what cube is better than the Aolong? I started to spend more and more money on newer cubes because I wasn't satisfied with my current cubes. When I got my next cube, the Hualong, it was so fast I was so impressed. After getting used to the Hualong, the Aolong feels like really sluggish. Still not satisfied with what I already have, I went out and bought MORE and MORE cubes, I got all the long series cubes and without even thinking got the Tanglong and Aolong GT immediately when they became available. Still unsatisfied, I got the Meiying, Gans 356, Yuxin 3x3, Thunderclap, and much more. Now? I'm just stuck with so many 3x3s even a octopus can't OH all of them at once. I don't even touch them anymore. I just use 1 cube, the Thunderclap, which is my main.
The moral of the story is, if you're already satisfied with your 3x3 and it isn't spoilt or anything, then just stick with it until you are absolutely sure the next cube you're gonna buy suits you the best and will improve your times by a huge amount, or your cube is some crap like the Guanlong (good for price but crap for me), then get a new one. Trust me, you will regret it if you buy a bunch of cubes you won't even use, UNLESS you are a collecter.