Curing Waltz is already pretty strong as it is and doesn't need any buff. But upping the range from 3y to y5 would be great. 3y is extremely small and and requires very precise stacking. 5y wouldn't break it, you still have to stack for it. And having dance partner earlier than 60 would be nice aswell.

But making Standard affect the whole party would be such a huge buff that they have to nerf potencies into the ground. Even on bad runs with a mediocre dance partner I get 850 rDPS through standard alone. With it buffing the whole party that would easily climb to 3k+ which would put Dancer in line or even ahead of jobs like SAM, BLM or SMN while having no uptime loss and full mobility, no positionals and almost no range requirements.