I try not to read more than one visual novel at once as I find it detracts from the overall experience for me, but I can't say that it's unusual for me to do the opposite of that. I think for me visual novels sort of go through a honey-moon phase. Once the initial excitement of starting a new read wears off, I find myself considering what I intend to read next and find myself more excited to read the new title than what I am currently on. I'm like a small child in a lot of ways.
This is usually for the more 'lightly read' stuff though. If I find something particularly engrossing, I make it a point not to dilute my current experience by trying to balance a handful of VNs. Things like G-Senjou, F/SN, and currently Grisaia have been good enough to singly hold my attention.