I’ve been in the same situation a few months ago (Odroid HC-1). I upgraded to a Pentium NUC7 with 16GB RAM, which has more than enough power and ram for my use. A huge improvement over the Odroid and it was pretty cheap too.
What’s your download rate? A high download rate is causing some CPU usage, I notice that on my build too. I’m downloading with ~120MB/s.I wouldn’t worry about 30% cpu usage, seems fine to me. Downloads might be served compressed as well, so you pc has to decompress them on the fly.
That’s definitely too much. I paid 128€ for mine earlier this year.