First off, the prices dropped because the market got flooded by players who once the shields lost their special abilities sold them off. Visages got heavily botted dropping the prices even lower. Its just how the market is sadly enough. I can remember when whips were in the millions now they are less than 100k.
So you can blame the EOC, The GE, Bots, Merching and free trade for making a lot of things lose their value.
As for your fix it might work. But then they would have to do it to all the rare or extremely rare items that have lost value too.
The current price for a draconic visage is 1,219,000. The visage is a very RARE drop from KBD, Iron dragons to Mithril dragons, and everything in between, Frost dragons,etc. So, a very “rare” drop, that was once worth “bank”, or atleast for most, is now worth a Dragon 2H (200k less). It would appear that in order for the price of visages to rise there needs to be an item sink, no? The fix that I have in mind is adding new Dragonfire shields. These shields will have added defense bonus’ then the regular Dfs’. These new shields will have not one visage, but two, or three, or even four. The shields could now be in tiers. The shields will not be able to be reverted. This could solve the visage problem much like how the new toolbelt feature made the dragon pickaxes and dragon hatchets rise. If anyone has any suggestions please feel free to post them! Thank you.
The problem is that Runescape EoC nerfed the Dragonfire Shield big time.
They removed its level 75 stats.
They removed its dragonfire attack(which was true dragonfire and not an ordinary magic based ability)
They removed its melee damage bonus.
They imposed massive combat triangle penalties.
Super Antifire potion is more useful for thoes that have it.
These nerfs pretty much killed it, and the ONLY thing the DFS is good for now is really just for fighting dragons if you can’t make Super Antifire pots.
So the solution would be to make it a level 75 shield again, give it backs its dragonfire attack and attach a crit or damage bonus to it once again.