I've not had the goldflame, but I used to chop down my regular white spirea every few years to "refresh" them. Te regular ones would come back fine.

Your goldflame will likely come back. But, if you put younger ones in next to it, it may always be a little bit bigger.
Why not get enough new ones to encircle your crepe myrtle, and move the one goldflame that has been "pruned" to another location? Your circle would be more congruent and that way if the "pruned" one doesn't recover, you don't have a hole in your circle.

Thanks for the advice and reassurance! Ironically, I had originally planned to just move the two I had behind the tree, then fill in with another perennial up front. So Marlin, I took your advice, mostly, and bought 2 2 gallon good sized plants to circle behind the tree, and will do a wait and see on these. If they come back, I can make a judgement call about moving them next year, if they are too big. If they don't, I can replace them. This is why I always "clean" and mulch my front bed, too many perennials for gardeners to pull out - but,boy, do my guys do an amazing job of cleanup.