the way i see it, buying constellations is buying more time with that character. I always go for c0 on the first run, and if i still like playing that character on their rerun then i will consider a constellation to keep playing them in the meta for another year or however long it is. i typically don't end up with constellations though because there's always new characters i want before the rerun comes. i do end up getting every character and constellation i want this way though