Update, when I had the chance to try out the longer 10-32 screws, it became obvious that my perception of stripping was correct, but only for the first 2-3 threads because that's all the lucid-supplied 1/4" bolts were grabbing. When I used the longer screws, a very positive engagement was found and I have no doubt that the license plate will stay on until Iremove it.
For attaching a standard plate with the Lucid license plate frame and the supplied "black buttons", the 1/2" long screw was the perfect fit (even in the top right corner where my metal registration tab is essentially a second plate).
For the front plate holder with just a license plate, (no frame, no buttons), it looks like the 3/8"long screw will be the right length.
Just remember that since the 10-32 screws are such a fine pitch compared to traditional license plate screws, it'll probably feel like it takes forever to tighten.... Just be patient and keep turning, though I don't suggest too tight.