This doesn’t address the visual beauty of flowers as such but, worth noting: flowers often emit chemicals that mimic the smell of sex hormones and their metabolites. Sex hormones are quite similar across the animal kingdom. This is part of why we like flowers and use them in perfumes. Other species do similar things eg truffles.
So the appeal to humans could, in the case of truffles, be a side-effect of an attempt by the fungus’s to get pigs to dig them up and spread the spores.
A fascinating book on this topic “The Scented Ape” https://www.amazon.com/Scented-Ape-Biology-Individual-Development/dp/0521395615/ref=sr_1_1?ie=UTF8&qid=1467162838&sr=8-1&keywords=scented+ape also it is interesting to read a few books about how perfumes are made.