To be honest, I think you underestimate how much teams want to be the league leaders. Huddersfield are really going for it. I know Wigan and Wire have in the past as well. It is a meaningful trophy at the end of the day, just not the big one.
IMO you either have a prestigious playoffs which determines the winner or you have a prestigious league which determines the winner. I'm not sure that you can have both.
Clubs and fans will know that the big prize is still the Grand Final, so you're taking a big risk in hoping that the league leaders shield will provide motivation to the clubs and the fans guaranteed to make the 8. If it didn't work, then we could have a real damp squib of a season for 22 rounds amongst the top clubs. I think the better balance is to continue the points into the second part. We could also see teams making the 8 comfortably but not being in contention and then resting their players in preparation for the second part of the season.
Your point about the 7th and 8th clubs is valid, and to be fair I think the whole system is flawed but if it has to be done I'd rather risk these having little to play in some seasons for than our best clubs.
I think the battle for top spot is definitely worth watching.