Super Takumar Quality Difference?

Besides the obvious difference in speed, is there a noticible quality difference between a 55mm 1.8 Super Takumar and a 50mm 1.4 Super Takumar? Also, how much difference do the later Multi Coated lenses make in in scenes not involving excessive flare?

Some Super Takumars (usually later ones with the additional lever in the mount) are actually multi-coated even though not marked as such. The SMC coating is very effective at reducing flare almost completely and it enables ever more complex lenses with high numbers of elements to be made. I don't think in practical terms you will notice much difference in non-flare situations, although the colour balance may be slightly different.

Both the f1.8 and f1.4 lenses are superb performers. The f1.4 lens is less suitable for use on bellows and reversed for macro work, because of its design. I would happily use either of these lenses, and have done so in the recent past.