Is Vivca+ 19 with costume worth limit breaking?
Why not? You can use her everywhere: titans, raid offence and defense, map stages.
The real question is: which other heroes are in your yellow stack that could be better than her?
well i have wu kong,justice and chao maxed,and currently working on gullinbursti
Gullinbursti is a good candidate. But I think that in short times you can do them both if you already have the 5stars yellow aether.
I would say Vivica in costume and at +19 is worth limit breaking.
She will continue to be useful in your roster
If you have costume Leo then him first.
If not then Jackal first.
You can do Viv and jackal with those eithers. (Seems like you got one tier 3 either from somewhere).