Great comments! I also think that a huge element that goes into what makes an effect "powerful," is what Vernon referred to as the "emotional hook." In fact, this might be a more significant factor than whether it is done in the hands versus visual. As an example, I learned an effect years ago (and I'm sorry I don't know who to credit for it right now) that involved borrowing a spectator's business card and having him fold it several times, with the magician pattering about how it involved doubling his efforts in business, which is likely to produce success. Already, this personal element, arouses interest, engages the spectator's emotions and draws him in psychologically - I guess you could say, giving him/her a stake in the trick. Anyway, after the folding is completed, magician takes the folded card momentarily from the spectator and accomplishes a switch for a pre-folded dollar bill and places the bill (they think the card) in the spectator's hand, immediately closing the spectator's hand over it with the request that he/she hold on tight so magician cannot get anything in or out of the hand. (Of course, the work is already done.)
After further suitable patter, such as asking the spectator to imagine producing wealth by his/her efforts in business and positive thinking, the spectator is asked to open their hand, where much to their delight, their business card has transformed into a dollar. Very shortly after performing this trick for a while, and getting a wonderful reaction, I realized how much better it would be to let them keep the dollar. Sure it costs some money out of my pockets, which aren't exactly lined with gold, but the reaction was exponentially greater, and the spectator feels great when you tell him/her to keep it as an omen or good luck token of more abundance to come. It means the world to them, as opposed to taking the money back. On top of it all, you now have their business card, and you can text or email them, if you like, to tell them how much you enjoyed performing for them, provide your own contact info, and to please keep you in mind for their next party or special event! Often, they will immediately ask you for your business card. Packs super light, happens in their hand, and provides a whole lot of bang for the buck!