Are upgraded power cables really worth the money?

Yes, upgraded power cables are a good investment. I admit I'm spending a bit more on them these days then when I first made a purchase. You can spend from $10- $12 on a Volex or thousands of dollars on the exotic cables. I refuse to spend that kind of money. I started out with lower priced cables from Shunyata, even the dirt cheap Volex, but eventually graduated up the food chain a bit. In my opinion, of all the cables you will purchase, the power cord can reap the most benefit and also do the most harm. So, auditioning in your system carefully before purchase is critical. As suggested, buy a cord you can audition for at least 30 days in your system. If you don't like what it does when connected to your gear, then send it back for a refund. There are companies and dealers that provide auditions. I would look to dealers that provide demo power cords that can be auditioned. Also, the Cable Company will lend you cables for a small fee. DCCA and VH Audio sell quality power cords, have great customer service and also have audition periods on all their cables. Don't make the mistake of auditioning more than one new power cable at a time. More than one new cable in your system at a time makes evaluation of each cord practically impossible. I also belive in power cable break-in. (some don't) It's important that you allow a new power cable break-in time and time to settle in once you connect it to your gear. As you know, once any cable is connected, it should be left untouched and given time to settle in. The sonics of your system will change during these periods. After break-in is complete and the cable has had time to settle in, then make your final judgement. It takes time and patience (which I never had a lot of). Good luck with power cords.

The Signal Cable Magic in my experience lacks smoothness refinement and extension.