As with everything, you're playing for RUBES, who haven't listened to the original that closely, and frankly don't care. They notice the (A) HOOKS and feel the (B) OVERALL SPIRIT. Those are really the only two things that matter. As fun as the rest of it is, that's all "musician's fluff". And realistically, if it had been recorded on any other week, a lot of those subtleties would have been completely different. As musicians, we often spend hours digging in to the exact parts as they were recorded, but also as musicians, we have the perspective to know that a lot of those timeless parts were created on-the-fly, at the whim of the band/producer who were likely VERY HIGH at the time. Had they had a different strain of Ganja or a different supply of Blow things could have turned out very differently. But the spirit is what matters.
So, as musicians, it's our job for the public to correctly identify the hooks that 95% are going to remember, and capture the spirit of the musicians. I think Superstition serves as an excellent example, and a lesson in restraint. You GOTTA have the main Clav part as it appears in the intro, the rest is all Stevie jamming out, and my suggestion is to jam out too. Don't play the notes, don't bother with learning the exact line, just bang those Tangents like it's 1699.
Trumpet/Sax parts? The reality is noone off stage cares what instrument is playing them. At the end of the day, you're a dude with a dull box copping a buncha cats with shiny metal horns, who would most likely be doing synchronized dance routine while playing. That's the truth. Even if you're so studio perfect that the blind Stevie Wonder can't tell it's a synth, it's not gonna have the visual or energetic impact. That's why I always gig with a trumpet... nothing is more kinetic to a show than a live horn, even if you suck (which I do). If that's not in the cards, throw the part to the guitar player and let him strut his stuff. I guarantee the audience is going to be more receptive to it unless you've got some serious stage mojo... I do, and that's why I'm the most sought-after player in this city, but I can't do it on board alone.