I think you are on a good track with Anime opening songs. Though some of the vocabulary is grandiose (too fantastical for daily usage) they enunciate each word and make it understandable so that Japanese kids can easily follow along.
As a side note, do you know the word 曲 (きょく)? 曲 means 'song' and is a great word to know because I hear it used by Japanese friends way more than 歌--which to me sounds a little more formal！
Some songs good for learning Japanese:
(they sing slowly and a LOT of good basic vocabulary is included)
Kaze Ni Naru
(an absolutely beloved song in Japan and the singing is clear and easy to understand)
Digimon Tamers OP
(very easy. And you speak Spanish, right?)
(this singer Yumi Matsutoya is someone you should check out!! This video only has English + Romanji so I put a link for the Kanji lyrics as well).
Nishino Kana - to LOVE [album]
(I can't seem to find any videos that have Japanese + English/Spanish, but her songs are VERY enunciated and easy to understand. I recommend doing some searching if you like her songs!)
(this channel doesn't have English subtitles, but you may find many songs you like, and the lyrics are slow and easy to hear).
If you are just looking for Japanese popular rock music in general, here are some bands nearly everybody in Japan seems to listen to who I met (not sure if they really will help you with the language):
One OK Rock, UVERworld, Sekai no Owari, Bump of Chicken, Asian Kung Fu Generation, Funky Monkey Babys, Radwimps.
OK that should be a start!