Huh? You don't just get another potion of x, you get an additional chance for the useful item y that you didn't get before. It affects all drops, and that includes so-called meaningful drops.
You get more crap, of course, but where exactly is the harm in that? ADOM players get crap all the time. They just let it lie there. If it doesn't weigh much, they'll pick it up and flog it at a store. All popular RPGs have crap. Diablo II has crap. Players just ignore the cracked battleaxes, but they'd miss them if they weren't there.
As an ADOM PC, the world does not exist to cater to your whims; if anything, it's hunting you for sport. Powerful items should be rare.
You describe "players don't get enough meaningful items through normal means" as the inherent problem that increasing drop rates - of "meaningful" items or not - is supposed to solve. Of course, in ADOM, there are always multiple solutions to any problem. "Get more items" is just the more comfortable one when compared to "Figure out how to use the items I have to do the job in front of me". At some point, players lose interest in the latter (because it involves learning, and that can get hard) and look for every way to do the former faster and with less risk, and that's how scumming methods become popular. And that's why scumming and grinding will never die completely, regardless of how you tweak drop rates for whatever items you like.
A slight increase in drop rates probably won't hurt. But ADOM should always reward the willingness to learn how to do without.