Will a high quality preamp really make a difference in sound?? Also speaker cable

Every system is a different, but a preamp makes a difference in my system, and so do the cables.

Using junk cabling is a sure way to prevent your system from being optimized, and evolving into something special. With the options available today, there’s no reason to risk the cables being the bottle neck of potentially good system. There are lots of good reasonably priced and DIY cables. Mogami, Blue Jeans, Carol, Belden, SKW, Monoprice, Audioquest, GearIt, and others. No need to spend a fortune, but good cables should be quite audible.

Yes and Yes.  

Yes to both

I think the preamp is the most important component in the chain.   I usually spend over budget when I replace a pre so as not to make a lateral move.  

Unless you've had a world class preamp swapped into an already good system. It's hard to explain how pronounced of a difference it CAN be.  May take trying a few but a great one can really elevate your system to a different level. 

What improvements are you looking for, what equipment and cables/interconnects are in your system now, what’s your budget, and are you looking for new or used?

You can’t fix a crappy amp with a better pre-amp the same way you can’t fix a crappy pre-amp with a better amp. Every component plays a role formulating the end result. The key is to get a clean sound signal from start to finish. Quality cables transfer the signal between interfaces without introducing noise or loss. The bottom line is crappy in, crappy out.

I agree with @oddiofyl that a good preamp is of paramount importance and a hard thing to get right. Simple tube circuits are the best solution I've found personally.

My amp has a non-working left channel...sent it back to the factory to have a look see and fix.   I looked around the room and noticed the expensive power cord for the amp was lying on the floor not doing anything.  Stupid 82 old me replaced the "upgraded" cord on the CD player with the expensive one that used to drive the amp and was bewitched by the improvement.....just ordered new power cables for the rest of the system. 

The preamp is nearly as critical to the sound of your system as the speakers.

Common audiophile wisdom - active preamplifier is extremely important.

Speaker cables, like everything else, are important too. My speaker cables cost new or used as much as my speakers. Perhaps I overdid it a little but I haven't had to replace them in 25 years, and my system now sounds incomparably better than 25 years ago with the same speakers and cables. But it's a modest system, both speakers and speaker cables cost $1500 new 25 years ago.

Back in 1992 I purchased a AR SP-9. It made a huuge difference! It opened up the soundstage width, depth and detail. All improved immensely! It was though I walked into the room of the performance.

Put world class preamp in any decent system and you will probably agree with me. It is a transformative experience.   Makes the whole system sound better and live up to its full potential 

There are many great speakers out there hobbled by a mediocre preamp.  Or a so so amp.    Lots....  Part of the reason we've all been chasing better sound.  

 I think spending as much or more on amplification than speakers yields great results.  

More on amplification, definitely more. Unless the very top level where it might get equal, I don't know. Give any good speakers a signal and they will sing.

Right now I'm using 2 identical Anthem power amps MCA 225, NAD C379 preamp, Cambridge audio cxn100, and a Marantz single cd player as a transport using the dac inside the NAD. As far as speaker cable I'm using some that I found on Amazon and it seems to get the job done, the name of this speaker cable is WBC.

One of the most  significant jumps forward in sound quality in my system occurred  when I made a substantial upgrade in the preamp. The only thing that made as much difference was room treatments. Like most of this stuff, it’s probably system dependent, and others may have had a different experience