Bragging rights, for aspects of the design which may or may not eventually make any sense, has always been the case for products sold to the innocent. I've read that beyond eight cores, memory management becomes so cumbersome that it's hard to get any better performance. Not sure if that's still the case, but it does suggest that migrating to as many as eight makes sense.
What also make sense is to aim for the same amount of processing power in these handhelds as one gets now from PCs. That's when one could conceivably start thinking in terms of docking the handheld to do the real work, and doing away with the separate PC entirely. Looks to like this is where we are heading. The problem is that until now, the battery life of powerful but portable computers has been pretty bad. I wouldn't be surprised in the industry is working hard to fix that problem.
Also, I don't know about 8 cores, but without a doubt 4 cores are a huge improvement over a single or even dual cores, operating at the same clock speed. I've seen that myself, with a single core 2.8 GHz PC vs a qud core 2.8 GHz PC. Like night and day, EVEN THOUGH the applications running on these PCs are not multithreaded.