I have my doubts. First, until 1160 Louis VII was married to Richeza's stepdaughter, Constance of Castile. After her death he quickly remarried to Adele of Champagne. After Alfonso VII's death Richeza's political position was relatively weak, since Alfonso's state was divided between his son from first marriage who weren't exactly fond of their stepmother. Richeza's only strength was her being part of the imperial family. Not enough, I think, to make king of France interested.
Regarding possibility of Richeza's marraige to Louis VII instead of Alfonso - no. Louis was married to Eleonor of Aquitaine until 1152, the year of marriage of Richeza and Alfonso, and negotiations concerning royal amrriage usually tok at least a year. Anyway, Richeza could gve her husband nothing but prestige.Marraige to a member of the imperial family might have been attractive to a Spanish ruler with imperial ambitions, even with no territorial gains. To a king of France that might have been not enough.