Steve Elliott
"I just took a look at the #3 blade I've been using, there is a very visible wear strip on the back, if it actually changes the bevel angle, I really doubt I would be able to tell when using the plane (I regularly push 45º to 60º planes without noticing much difference in effort)."

When a plane blade needs honing the main issue is loss of clearance behind the blade. The rounded wear surface behind the edge is being pressed down into the freshly planed surface of the wood. Honing only the bevel solves this problem even if it doesn't quite give as sharp an edge as a thorough honing of both surfaces.

Your description of the wear on the upper surface of the blade increasing the cutting angle is exactly right unless a cap iron is set very close to the edge. With a cap iron the wear can actually cause a decrease in cutting angle due to a hollow in the upper surface of the blade where the shaving is being bent sharply. Just this week I've been reading a study published in a Japanese technical journal that has scanning electron microscope images of worn blades showing the wear caused with cap irons set at different distances from the edge. Here's a diagram based on the SEM images showing a typical case:

The scooped-out area on the face of the cap iron edge is due to wear after planing 200 meters of birch. This cap iron had a microbevel of 50 degrees and was set 100 microns (.004") from the cutting edge. The study concludes that a microbevel of 50-60 degrees set 150 microns (.006") from the edge gives the best cap iron effect.

Returning to the issue of clearance, here's a diagram based on my own wear profile images that emphasizes the loss of clearance:

So honing only the bevel will help a great deal to freshen up a working edge because it restores clearance behind the blade edge.