From my recent experience I'd say YES! Earlier this week I swapped out my separates for a decently reviewed receiver that I had bought 3 years ago. Always thought this receiver had a rather 'opaque' sound along with the tonality being off as well, and it wasn't sounding any better this time either.
Decided to try some of my better interconnects in place of the metal preamp/main jumpers and WOW!, what a change. Really surprised at the difference with my better silver or hybrid copper/silver interconnects. My more lowly interconnects didn't fare nearly as well. Now I'm looking into making some custom jumpers. AudioQuest has some premade one's for around $30 but I think I'm going to try my own first. Just need 4 RCA plugs and some good wire (I'm going to try teflon coated) connected just to the positive center pin of each plug.
I had seen people mention the problems with these jumpers before but didn't expect the change I heard. I recommend trying this.