Is it worth spending extra to get a nicer circular saw?
I wouldn't worry so much about blades flying out, even when using a cheap harbor freight saw. What is more likely to happen is the motor will burn out quicker than a quality tool. I've bought many harbor freight tools for "time to time" use. I've got a drill press that's lasted quite a long while ... granted I only use it a few times a year so I got my money's worth.

I think you'd be fine with the cheap saw as long as you're not going to use it all that often. The blade won't come flying out but the motor will probably burn out and fail long before the DeWalt motor would.