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KAuss, I transferred your posts to a decision matrix.
From the variables you're considering, fuel economy repeats most often. You're also concerned about a possible 86 v.2.0 appearing in a couple of years, so maybe doing some minor repairs on the X-Runner and waiting it out is a reasonable alternative.
Meanwhile, consider a used Prius with an HOV sticker to save gas and time (tint the windows so people won't mock you but it's the Bay Area so could be seen as virtuous) and sell, save, or store the X-R for pleasure or utility. Then sell the Prius should a new version 86 appear.
If you're thinking of track days, many tracks no longer allow roadsters without SCCA approved rollover protection, a strike against the MX without a bar/cage/hardtop.
Others mentioned how to drive around the torque dip on track by keeping the revs up and it works. It'll also eventually teach you momentum driving, a valuable skill in a relatively underpowered car that compensates somewhat at corner exit while you finesse the car at corner entry and through technical bits.
On the street, a TRD CAI helped throttle response and smoothed out the dip on my FR-S combined with a Perrin catback. Expensive though, and the TRD CAI may no longer be available for '17s+, so try a TRD air filter first.
Or forget the whole thing for now. New car sales have hit the wall this year so expect generous cash incentives closer to model year changeover. Already in my area, some 86 TRD's are listed for $30K, about $4K below MSRP.