How is this motorcycle street legal?

Well depending on your state, you may only have to add 1 mirror or you might have to add both left and right mirrors. as to which one-how would I know which one fits you better? You are the only one that can decide which bike fits you better-reach to handlebars, stretch of the legs to the ground etc. as to will either keep their value-depends on how you use them or abuse them. Better kept machines command the best money, beat up machines go for a lot cheaper.