“Luster” is an optical property of a gemstone and since a synthetic stone has same chemical and optical properties their luster will also be the same. The only thing is that synthetic gemstones are generally more clean and clear than natural counterparts that are why synthetic stone seems more appealing.
People wear gemstone not only for astrological power but also for status symbol and pleasure i.e. why they go for natural one. If I have been asked to wear a gemstone, I would also go for natural one because it gives me personal satisfaction. But if the price is beyond my reach then I wouldn’t mind going for a synthetic gemstone. It’s actually ones choice.