For the sorts of lengths that you'll be using inside of a room in your home, there's
almost no chance that an RCA cable will make any difference. I mean, it would have to have something seriously wrong with it for it to make any difference. There's really no need to buy a new cable unless the cable you have isn't long enough, or it's too long and annoying to manage
That said, monoprice.com and tartancable.com (Tartan is a sub-brand of Bluejeans Cables) are so inexpensive that if you just
want a new cable, it costs almost nothing!
What I would do, I would wait for a time in the future when you need (or just want) several new cables. Maybe you'll want/need a few HDMI cables, some optical cables, maybe an F-cable for your cable box/cable modem, some ethernet cables, USB cables, or one thing that can be really nice is to get some shorter-length IEC power cords so that you don't have to wrap or wind up all that extra power cable length that makes a spaghetti mess behind your gear! Wait until you need a bunch of stuff like that and then just make a single order from monoprice with all of that stuff at once! You'll save on shipping costs that way
But for now, unless you notice an obvious hum or have some sort of connection problem with the RCA cables that you have lying around the house, there's no need to buy a new cable. Placing an order, even when it's so cheap, for just a single cable always feels a bit silly and it really isn't necessary. But you'll probably have a time in the future when you could use a bunch of different cables, so just throw in an RCA cable when you make that order one day
Like I said, they're so cheap from monoprice, and it never hurts to have some good, extra cables around
