I'd say a covert ebike is probably a "luxury" upgrade. It's hard to call it a "performance" upgrade because then you could justify any motor as a "performance upgrade" and end up with an eMoto. Which to be fair, many people do. But the spirit of the ebike is probably moreso to allow you to keep up with faster people who ride normal bikes and/or flatten hills so you can always hold a consistent speed and/or cover a greater distance.