How bad is the Latin Spanish dub of Kai? I can definitely see it being a downgrade from the Latin Spanish dub of DBZ because...
1. Their DBZ dub was uncut, whereas their Kai dub was edited.
2. Their DBZ dub was based on the original Japanese version, whereas their Kai dub is based on the Nicktoons-censored English dub (even keeping the English title cards).
3. The Kai dub had a ton of recasts due to budget issues.
...However...honestly, I've seen some clips of the Latin Spanish dub, and the acting, in and of itself, seems to be quite good. The new Goku in particular, Edson Matus, really sounds emotionally invested in his scenes. Since I don't know a lot of Spanish, I can't say for certain, but at times he sounds like he's actually more into it than the original Goku, Mario Casteneda. Here are some examples.
1.
The Makankosappo
2.
Goku uses the X20 Kaioken on Freeza
3.
Goku spares some energy for Freeza
4.
Namek explodes
EDIT: As well-done as the acting was in clip 4, I don't think I'll ever be able to watch this part of DBZ ever again without thinking about the Muffin Button.