But there is a big difference between a tank which has not been properly maintained (i.e. regular water changes and healthy plant growth with nutrients added as needed) and a tank that HAS been maintained properly, but has an old substrate. Below is a link to a tank that I just stripped down, not because the fish weren't healthy (I regularly pulled bags of Cherry Barbs out of this tank to sell to the LFS) and not because the plant growth wasn't good. (you can see that in the photo). I am getting rid of the tank because it is over 30 years old, and I am worrying about the silicone seals.
The tank has been set up with the current substrate (1-3mm quartz gravel plus laterite, a handful of peat, and, of course, by now, LOTS of mulm and organic material from the plants themselves) for about 20 years.
Over that time, probably about 4 times, I loosened the substrate by removing the plants from about 1/3 of the tank at a time, gravel vacuuming that section, and replanting. I did 1/3 per month until the whole tank was done, and it was good to go for several more years. (this is a technique taught to me by Claus Cristensen of Tropica).
Just wanted to show that tanks with a good substrate can be very successful for a VERY long time!