Are There Improvements that Can Be Easily and Quickly Made Without Buying More Stuff?

Great advice from Chayro, I love Graceland by Paul Simon and So by Peter Gabriel, , unfortunately they both sound terrible on any decent stereo I have tried, much, much too bright.  Sorry, goodbye Peter, goodbye Paul.

+1 for earwax removal.  Sounds silly but once you try it, you’ll understand.
Avoid q-tips whenever possible.  Just use something like Debrox and then shower.
Almost free.   

I would do a complete cleaning with few affordable things: pipe cleaners, microfiber cloth, electrical contact cleaner & canned air. Step 1 disassemble the entire system and throughly dust and clean the shelves: Then use microfiber cloth to clean the outside of you components. Then clean the outer portion of the rca's with electrical contact cleaner & microfiber cloth: Then use a pipe cleaner and electrical contact cleaner to clean the inside of the rca's. If you have XLR's, the pipe cleaners work great to clean both male and female ends. The you can use microfiber cloth and electrical contact cleaner to wipe all the blades on your power cables. Lastly, you can turn your attention to the speaker connectors at the amp & speakers. The pipe cleaners work great with banana connectors & the microfiber works great with spades. Once all this done, you can reassemble the system. Then final thing to do is to use the canned air to blow out the volume control and all the buttons. This deep cleaning is good for 1 year with minor maintenance. 

No. You always need more stuff. And keep it clean by taking it all outside and blasting it with a powerful leaf blower.

Check the torque on your speaker raw driver bolts/screws.

This was suggested a while back by a member.  After a quick check I found myself tightening 96 machine screws holding the speakers in place, ranging from “not quite snug” to “suspended in space, not performing a useful purpose.”

Worth checking out.