To me it seems like a shame that something that pops up so readily in the game as drops due to their viability way back when and due it their simply not having been removed completely (since that might not be the easiest of things to do coding wise).
Still how could one make the DQ item above 30 have some viability without creating issues due to botting... one of my suggestions stems from what you can do with level 20 and level 30 DQ Items -- simply expand upon this concept. Currently 5 of each DQ-20 gets you 1 (8 slot) Bank Expansion (BE) and 10 of each DQ-30 gets you another (8 slot) BE. Considering as folks gain levels having additional Bank slots could be quite useful why not continue with this concept such that 20 of each DQ-40 gets 1 (8 slot) BE (bank expansion); 30 of each DQ-50 gets you 1 (8 slot) BE; 40 of each DQ-60 gets you 1 (8 slot) BE; 60 of each DQ-70 gets you 1 (8 slot) BE; 80 of each DQ-80 gets 1 (8 slot) BE; and finally 100 of each DQ-90 gets 1 (8 slot) BE
This still leaves 2 (8 slot) BEs that have to be gotten via Stones and does nothing to improve Inventory, or Cupboard space just gives long time players a bit more room and perhaps entices them a little to get those last two Bank Expansions and/or additional Inventory space. Plus it does not seem like it would make DQ items exceedingly valuable since eventually you will have the slots. Further some folks might be impatient and just use the Boutique method regardless.
Or instead of additional BEs what about perhaps replacing the Hay with DQ Items for the Pet Bag and or re-purpose the DQ items to allow you get get additional other expansions depending on how PWI views the worth of various expansions. This method would make DQ items at least worth acquiring but not make them something that is worth more than coins which you can auto-bot for fairly easily.
Or maybe just give them a value of something greater than 1 coin something proportionate to their level. DQ-20 5 coins, DQ-30 10 coins, etc... again whatever PWI deems an appropriate coin value for something that drops at the level of where each DQ item drops although this seems rather dull.
Personally I think it adds a nice dimension to the game when you have things to collect and trade because you need so many of each but you only have some of them and not all of them. Perhaps a more complex mixology could create a interesting use for the DQ items kind of like an exotic crafting recipe that uses DQ items. I mean they seem like such a ripe game piece to do something with -- it just seems like a terrible waste that nothing has been done with them since the dropping of the Dragon Quest concept.
If you have a suggestion of what the DQ items might be used for please add your thoughts but keep in mind it has to be something that is fairly balanced or PWI will never go for it. Further if it would require some great change to implement it most likely wont be viable. Just food for thought in case you do make a suggestion.
Hope to see DQ items make a come back in some fashion