I like to bring heroes to lvl 9, as it gets them a couple turns through the talent path. For heroes I use less often I’ve given them +1 for the talent unlock. For my strongest heroes I’ve pushed them to +11 to +19 depending on the hero, class, and last nodes.
It can be expensive to reset and reallocate, but unused emblems sitting in inventory don’t do you much good. I’ve done some targeted embleming of heroes I knew I’d reset but in the meantime would be stronger heroes. Spreading emblems like that early as part of a plan gives you a boost and keeps the investment from being too costly so you’ll get a clear return.
I also emphasized 4* for a long time and made key heroes pseudo 5* to compliment my 5* heroes. That helped in raiding but more so in wars. Some 4* will keep their emblems forever, but as my 5* gained strength I’ve shifted some emblems and effectively retired the 4*.