Overall, probably not worth re-taking. Is the student “hooked”, meaning are they in a favored admission group? This would be an underrepresented minority (Black, Hispanic, Native American or Pacific Islander), the child of a wealthy donor, a recruited athlete, come from a geographically under-represented state (like Idaho), from a poor background and first gen to college, or possibly a legacy? Then those scores are good enough, and if the rest of the application is as you say, they might have a good chance.
Does this student have a “spike”, meaning extraordinary achievement at the national or international level in something that either the college wants (already publishing scientific research in Cell or Nature, or dances with a big city ballet company, or is an Olympic athlete in a sport that isn’t a recruited athlete sport, or won international level music competitions, that sort of level of achievement)? Then it is likely that with the caliber of the rest of the application, they have a chance at acceptance, and they don’t need to retake the SAT or the ACT.
Is your child all that you say, but has neither a “hook” nor a “spike”? Then a 1600 or 36 will do no more to get them admitted to a top school than the 1530/34 that they already have. They should probably submit the score that looks higher percentile, shows a better score in the discipline that they intend to study, or doesn’t show a serious deficiency. The only exception to this that I would make is if your student did much worse on the science section of the ACT than the other sections. The reason that I say this is that the science section is not about science. It’s about data interpretation, and a little prep by doing old ACT science sections would familiarize the student with the charts and graphs that they use, so that a student of this caliber could likely bring that subsection up to a 36 with just a bit of self-prep.
Your student’s time is best spent at this point on trying to bring an EC up to appear to be on the national level, essays, and choosing safety and match schools. T20s were a crapshoot this year for anyone who wasn’t hooked or spiky - many students with top grades, perfect scores, a string of AP 5s, captain of varsity sport, accomplished musician, etc etc etc didn’t get into ANY T20 schools and are going to their safety or a match, if they’re lucky.