Interesting discussion, I wonder if anyone has done airflow testing in a wind tunnel using smoke to show the airstream.
Been done with smoke for flow visualization, with pressure taps to measure chordwise pressure distribution, and by other testing forms. And depending on how old you are, this research was possibly begun before you were ever even born.
What you are talking about is classic subsonic airfoil theory, and lift coefficients, and drag coefficients, and other aerodynamic characteristics. I can highly recommend a book like
Theory of Wing Sections by Abbott and von Doenhoff for some explanation and a ton of airfoil data. (Amazon.com for under $10) Or see if your local community college offers any instruction in basic aero, if you are really curious.
Long story short: a rounded leading edge (LE for short) makes a significant difference in airfoil performance versus a square LE.
Long story still long: Actually, a square LE has the general aerodynamic characteristics of a "flat plate" airfoil section---which stinks. The round LE needs to be smooth (as does the rest of the airfoil surface) and the fin thickness also needs to taper from root to tip in proportion to the local chord. The LE shape should ideally be more of a half-ellipse with the LE shaping extending back to 20-30 percent of the local chord. On the rear half of the chord, the thickness should again taper down to a thin trailing edge (TE) on the ideal airfoil. You should end up with a cross-section that looks like a stretched-out teardrop.
On a more practical note, LE shapes for subsonic model rockets still work nearly as well with a simple rounded cross section that extends only 5 or 10 percent of the chord, a wide zone of flat fin shape back to 80-90 percent chord, and a taper down to a sharp TE across that last 10-20 percent. This is only really important if you are building a competition altitude or duration rocket. The thin fin TE shape will damage more easily and for "sport" rockets many builders trade off the improved durability of full-thickness TE shapes against the drag reduction and extra performance of tapered TE shapes.
Then you have the even more practical aspects of airfoil details like the Gurney flap. Race car driver Dan Gurney found that if he added a short flap at the TE (perpendicular to the chord) that he got more lift (or down-force, for a race car driver) with no measureable increase in drag, which goes completely backwards from classic airfoil theory. Other experimenters have found that they can still get most of an airfoil's aero performance after increasing TE thickness from a knife-edge to a measurable thickness (which is easier to build), which also goes completely backwards from classic airfoil theory. Finally, you have wings on things like insects that operate at extremely low Reynold's numbers, generate lift just fine, and look exactly like flat-plate airfoils with rough surfaces (hairs, blood vessels, etc). Go figure.
Our model rockets don't (in general) quite fit into the extremely low Reynold's number class, unless you count modroc BG and helicopter wings. Our rockets are big enough (and have long enough fin chords) and fast enough that classic airfoil shaping rules still apply. Even the highly swept designs (which get into three dimensional flow effects) still benefit from a rounded LE shape. Yes, it's worth taking the time to do a little LE shaping.