For me it really depends. If I'm listening to Japanese music, I care about the lyrics, but not as much as I would care about the lyrics in an English song xD It's not like I can understand Japanese anyway
I love a lot of songs with meaningless lyrics (WoWa, anyone?) but if a j-pop song has great music AND great lyrics, then I'll love it even more ^-^
So yeah, in the end, I'd prefer to listen to a song with meaningful lyrics, but they're not necessary for me xD