Think a little harder about what is going on in the transmission, you are on the right track though.
With the engine running and transmission in neutral. Input shaft is spinning at engine speed. Under normal conditions, when you put your foot on the clutch, the drag of the gears will slow down and eventually stop the input shaft from spinning. If you attempt to put the car into a gear with the input shaft still spinning the syncro will create additional friction and stop the input shaft from spinning. This phenomenon will result in an initial resistance to going into gear and as the syncro overcomes the inertia of the input shaft it will allow the gear to go in. If on the other hand, something is keeping the input shaft spinning then the syncro not only has to overcome the inertia of the shafts but also whatever is dragging. This could be a pilot bearing or a slightly dragging clutch. It doesn't take much on an 11" clutch disc to overpower the tiny syncro's friction surface.
This is why I suggested putting the car in the air. If you have the car running in neutral and you try to put the car into 1st gear (with the clutch in of course) and the tires attempt to turn, then you have a dragging input shaft and/or clutch. Just to make sure, hold the clutch in for several seconds before engaging first gear (this will make sure the input shaft has enough time to stop turning if it is going to be inclined to do so.
If you don't feel that a dragging input shaft is the problem, then I suggest that you add friction modifier and go out and drive the car a little and see if it quickly improves. It won't work imediately because the fluid (friction modifier) has to have some time to mix and work it's way into all the syncro surfaces. It should work within a 1/2 hr of normal around town driving going "nicely" through the gears.
Generally the blocker rings themselves don't show any wear on rebuild. Usually I only see visible wear on the reverse blocker. I've seen some so bad that they have no points left at all and in fact I had one so bad it got stuck and wouldn't slide. I was able to "repair" it with a die grinder. I did not attempt to rebuild the ramps, I just used the die grinder to take away the "folded over" metal on the teeth so it would slide freely again. So ya, if the teeth aren't really nice anymore you may have problems that nothing else will fix but it would have to be pretty bad IMO.
I say put the modifier in it and go drive it around a little.