Will the sound quality deminish over the years?

The OP inquired about loudspeaker degradation over time. Instead, he gets a discourse about tuners. Kijanki gave the only useful response.

Foam driver surrounds deteriorate and need replacing. How soon depends on the heat and humidity of the environment in which they operate.

I hope this helps.

The sound of the system can change quite a bit day to day and we often don't notice. How can you expect an audiophile who's constantly changing things around to notice a change in speakers over a very long time? Doesn't make sense. He will have replaced all his cables and all his electronics at least twice! Hel-loo!

I guess what started it was watching how to realign a coil video. It made me think of what else could happen including maybe the crossovers getting out of spec through corrosion or heat.Seeing how cartridges have a lifespan of 2000 hours, if speakers degraded, how would one know how old they actually were? Gathering by some of the last responses, I take it,not to worry if a speaker is 20-30 years old.

"11-10-14: Mceljo
Zd542 - I didn't suggest that the change wasn't real. I did, however suggest that when his perspective changed he no longer viewed the Marantz as lacking highs, but rather have a more full mid and bass range. The sound of the Marantz was constant, but his assumption about it changed resulting in a different experience."

I think you may be right. Reading Nonoise's posts, I thought he was kidding. Reading them again, I'm not so shure. If he was being serious, I agree with you.