It is not a waste of money to go to a vocaloid concert because you are getting experience and having fun. Although it is a voice synthesizer, it is still a fun experience and I think it would be worth the money to attend and see the difference between a real vocal artist and a synthesizer.
No, attending a vocaloid concert is not a waste of money as it is up to an individual person to determine what is and is not a waste of their time and money. If a person will find enjoyment from attending such a concert, then they are free to make that decision.
If people really like Vocaloid they would be the ones going, waving a leek glow stick around. If you really like the music and have seen some of the high quality concerts on YouTube, I suggest you go since it looks like a cool rare experience. The only downside is that they would probably cost a lot to cover equipment and to pay all those who worked so hard to help program it.