If you can even mount an argument about it, and the card is in the design phase, you should reword it so it is abundantly clear. That's part of good, quality game design. It doesn't matter if players can make a correct, unambiguous decision using a full and complete understanding of the official rules (well, you are even worse off if they can't, but that's not "the bar"). Where possible, you should make the card so clear no one asks questions.
"You can't buy this unless you have a Magic Lamp in play. When you gain this, trash all Magic Lamps from play" is the same number of words and has the same exact play aside from Border Village, Storyteller, Black Market, Horn of Plenty and Haggler, which is a 5 card list but I'm pretty sure is in single digit percentage of boards.
That's another thing, you should make it abundantly clear whether you trash all Magic Lamps from play, or just one. "Trash Magic Lamp" is like, only one has ever existed or will exist so it doesn't matter.
Ok, I thought of the night cards too, Vampire and Changeling. The other option has some word cost, "When you gain this, trash it if you don't have a Magic Lamp in play". But it works with the rules more gracefully.
Or if you want to be super Melvin (is Melvin the name for people that like dovetailed mechanics? Vorthos vs. Melvin I think it's called) "When you gain this, trash it or a Magic Lamp you have in play."