Yeah, I know, you heard this one before right? Well, read on, because maybe you haven't.
Having two irons for doing a broad range of work with an old Stanley plane is very common. One iron for heavy work, and one for medium to fine work. In fact, it is one of the recommendations I give to beginners, or those getting into hand tools for the first time, because they can save money and still get stuff done. That is exactly what I do, however, the irons I choose are the real secret.
I generally like to keep and use the original thinner blades. There is nothing wrong with them and their thinness can be an advantage. The second blade I use is one from Veritas (usually O-1 steel), but you could also use a Hock blade in the same way (they're both ~3/32" thick). The point is that it is thicker than the original blade.
In the picture above you see two blades, one with camber, and one without. The cambered blade is the thinner original and it has an 8" radius curve for mass stock removal. This is important if you thickness by hand, or need to do some quick one side flattening of a board to put it through your thickness planer.
The new thick blade is sharpened relatively flat, with just the corners relieved, and can be used for general work, or smoothing.
So, why two blades of different thicknesses? Answer: Because now I don't have to move the d@mn frog ever again. Yeah, I still have to turn the screw for the lever cap, but that just take two fingers. The best part is the range of work that can now be done.
Now here is the trick, if there really is one. With the frog of my #6 Stanley set back all the way, I can switch out the blades to do all the work I need. The thinner blade opens the mouth enough to take a .05" shaving, which is nothing to sneeze at, and in fact thicker than most people can comfortably take on hardwoods. The thicker blade closes the mouth and allows me to take a .003" shaving without even trying. I could get thinner if I needed too, and the mouth is nice and tight. Now, the important thing to note is not the thickness of the shaving necessarily. The thing to take from this is that you can effectively do a wide range of work with little setup time between blade changes, and the change in the thickness of the blades actually opens and closes the mouth for you.
I know I didn't invent this, but I don't hear it spoken of very often in this way. Give it a shot and see what you think, might just save you some money and time on another plane.