I guess the weak link in my chain of mental processes is precisely the one you have just mentioned... Campbell can rock Guzman and from that point on, determine the way the fight goes. Not that the jump from 130 to 135 is that significant like it was proved too many times ( Pac-D. Diaz recently, Mayweather-Castillo, Corrales-Casa, etc) When I think about Soto and Barrios, it comes to my mind that they r rough and tough and not that they have a big punch. But I consider that they could have controlled the course of the bout had they landed that big one and had taken it from there... Happens, just the way you have put it, that they could not connect efficiently or followed it up cause Guzman beat them to the punch and boxed them on the subtle move. Nate showed to be sharp, consistent and solid with his and J D Jackson's game plan of fighting inside and in Nate's southpaw stance, present a side, connect and clinch himself on Diaz, roughing him up and stealing space so that the Houston boy could not swing freely. I don't think he can use the same strategy and physical attributes in this one - it doesn't matter if you are strong and athletic at close range if your younger and fresher opponent is going to stick and move... Nate is 36 and he has to look for the fight, it ain't gonna come to him like against Diaz in Plaza de Toros, Mexico.
Campbell-Guzman could be an interesting one indeed. Guzman to edge it, though I don't say it with total conviction. Campbell's power might put this back on a fairly even footing.
Though I doubt JMM still has power to beat Casa, still he will win on points. Casamayor shouldn't have picked a fight for Marquez, a Katzidis rematch would be more interesting than this. I would pick Nate as victor over Guzman, as the latter would usually go for a decision win. This two fights this weekend is absolutely shouldn't be missed.