No. Bad idea, no offence. You could just sell any upgrade you won't use for your next game and buy the ones you'll need. As Alex said, you'd basically have every upgrade.
However, I've had the idea brewing in my mind for some time that you could sell upgrades, but at half price or something crazy low. I'm sure there are people out there who regret buying stupid upgrades as a rank 4. I probably would have suggested this a while ago had our SP not been reset.
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"If in other sciences we are to arrive at certainty without doubt and truth without error, it behooves us to place the foundations of knowledge in mathematics."
-The Opus Major of Roger Bacon