RE: Splinterlands - Splintershards SPS needs more use cases in order to capture real value

do you think (or know) will it be the case in GL Goals GLX gameplay, too?

I don't know, but it is probable.

what is your experience, which one is giving higher returns? SPS pools or card rentals, playing the game???

The most profitable option is to rent cards. Returns are similar to SPS, but cards are more resilient to price drops. I prefer to play with my cards though, because I like to play Splinterlands.