First off...I won't tell you that the HF is the lightest model, since we all know that already. Within that realm, the lightest of those are not ONLY the the '88 (for second generation CRX's), but the early '89 as well. 89 is a tricky year. Mine is an early '89, but a change occurred at some point in '89 where the later ones DID have the seat belts integrated into the doors. This made for heavier doors & more frame support. This also carried over through 90 & 91 models. Secondly, you said "...gains over the VX's approx 52 mpg"...but what you should know is that IF you get the correct (Low altitude) model HF, your HF gas mileage should already be 52MPG (hwy) / (49 city). So you'd actually be hoping to achieve as high mileage as an HF, since the VX gets ....49? Anyway, I suppose the major advantages are the weight you'd save, the aerodynamics, and the fact that the VTEC-E motor has that fuel injector shutoff. And just imagine, if you did need to kick the secondary power in...it would be an HF that could actually get out of its own way! (amazing).
my leading thought with sugesting a non-hf modle of crx, is that it seems like the world would come out farther ahead if you took a car that was getting in the mid 30's to low 40's and swaped engines to get 20-30% better mileage, insted of taking a car that already can get in the low 50's and only improve it by a few percent, the crx dx is under 2,000 pounds, and with a few parts swaped could be made lighter.