I could never really tell much differences between interconnects, but for me, speaker cable was different. First, "18 gauge zip cord" is good enough, and seemed fine. Then, "Monster Cable is best", so that was next. And I did hear a nice improvement, over zip cord. Finally, let's try the "high end" stuff. High end, for what I could afford, was Kimber Kable 8TC. Now that stuff was awesome. Much better than Monster (IMHO), with crazy bass response. I still use it.
Now as to Monster, I think they've spread themselves too thin, trying to market to too many diverse markets. That, plus the fact that there are just too many available competing products now, no one company can dominate anymore. Even years ago, Acoustic Research, had a one third market share of every loudspeaker sold! That's insane. Now, they're a almost forgotten name brand, on cheap stereo cables, and even cheaper blue tooth speakers. Sad. But, you have to adapt with the times, to survive.