My house rule for shops is: Draw 3 cards and the investigator can buy whatever they want out of those options. Whatever is not bought is thrown into the discard pile.
I'm guessing the motivation for that rule is to speed up the game. I've seen things come to a screeching halt when a new player has to study the whole Town Item deck while everybody else waits, so it makes sense.
Personally, I prefer to encourage players to look at the deck when it's NOT their turn, and to basically plan ahead for what they want to buy. I also just let the next person go ahead with their turn while a newbie is browsing the menu (especially in co-op or at least non-cutthroat games).
I don't really like your solution because it takes away important tactical options -- some characters simply must have access to the Tools of Science or else their chances of winning are unfairly demolished. Also, while I told the OP that discarding a used Town Item would not impact much, I have to now say that discarding an UNUSED Town Item is a big problem. You could lose the Tools of Science before anyone buys them, not to mention other important items like Silver Shot or the mystery-cancelling Book of Lore, which has saved many games.