Is there a way in post to simulate the effect of a slow shutterspeed shot that leaves trails behind bright things in the shot that are moving. I was thinking if I recorded something at a high frame rate then used some sort of compositing filter that multiplies the frames that might do it. I feel like that would also cause darker things in the frame to also come out blurry or leave trails. Here's an example of what I'm trying to reproduce with a sparkler from a pit bull video example
Try the Echo effect. To avoid echoing the darker portions, duplicate the source and apply the echo to it; experiment with the compositing modes and also layer opacity.