Well, I went through their "guided tour" and didn't see anything about simulating the circuit, just some basic automated validity checks. I used to have a program for my old Apple][GS, when I was very young, which is the closest thing I've seen to what I'm envisioning. I know such simulation software must exist, but from what I've seen it seems to be mostly targeted at professional applications and massive projects, which is fine but would likely be overwhelming to many novices starting out and just plain overkill for many small robot projects.
Basically I'm wondering if there's an untapped market here (however small). My simple circuit simulator would be able to stand alone, but it's greater purpose is to support a 3d robot simulator I would develop later. Again, this would be designed to target hobbyists, people designing BEAM robots and other simple autonomous bots rather than professionals developing more complex commercial or industrial robots. Basically it'd be a way to rapidly prototype chassis ideas and allow easier testing of software by eliminating the need to reprogram the bot to test every minor change.