Better still is you use some foam between the two pieces of velcro to help cushion things a bit more. I do this frequently but only use the "hook" part of the velcro to better grab the foam. By itself velcro will isolate from vibration fairly well, but once you pull a zip tie tight the ignition box is pretty much directly against the wood and absorbing a lot of vibration, velcro or no. I agree about the mounting lugs. I tried that just once with one of the new type ignitions and the mounting lugs lasted maybe 2 flights. It may have failed on the first but I didn't look until after the second. Fortunately I used a zip tie as well since I did not trust the lugs.

Even better would be to use the velcro and foam between the box and the firewall, then use velcro to wrap around the box, securing all, but that would take a fair sized cut in the wood to pass the velcro.