Is the "quality" of the FX from the Sp 303 altered any, if you just run gear THROUGH it via EXT Source, as opposed to sampling INTO the 303?

For instance, would an effect sound fuller if a sample was sampled into the 303? Or would it sound exactly the same if you were running an external sound source through the 303, while applying an effect, but let it pass through and record directly into the PC, instead of into the 303?

No

yeah its definitely a bit different when sampled in to a pad as opposed to just running sound through, varying amount of difference for different effects too, i'd say the effect is more "pronounced" when you sample in, but its not always that simple, just gotta experiment and try both ways for different things to see what works/what you like

its different, and it matters more for certain effects.

Super good question regarding workflow efficiency. If anyone can elaborate on what the differences/experiences are please

dunno about effects but samples definitely sound dirtier when you record in. grainier and jellyish in a good way

Yeah, because when you record into the machine the sound passes through the fx processor and the D/A converter which is 20bit and uses Rolands funky RDAC compression. Sample that shit yo!