Having had a few cars of almost this exact vintage and style...
-- Air up the tires (free!)
-- if the tires are not all that good, get some good LRR style used tires ($50 total) put on the beast
-- check alignment ($20 if you know the right mechanic if not free!)
-- new air filter (if needed, $5 to $10)
-- stay under 35/45 mph if possible to avoid needing any aero mods (biggie and free)
-- pull the plug on the a/c clutch in the summer (if it even still works, free)
-- consider disabling the secondary jets on the 4bbl carb...it will be a bit slower, but then if someone get a bit throttle happy, it won't matter as much. (free)
-- definitely advance the timing as much as it will tolerate w/o pinging (free)
-- check for brake drag & repack the front bearings
----- Get a good vacuum economy gauge and mount it on the dash ($50?)
Otherwise, if it is being driving so little, but hauling so much, it is doing EXACTLY what it was designed to do...and with a little bit of patient driving, it might get up to around 15mpg...but don't count on much more...12 isn't too bad for a 25 year old tank around town!
Now...if they can plan their driving, and make it a fun contest...they might hit 20mpg. It can be done, but realistically, with several college age drivers...15 is a really good goal...and at $3/gallon for 50 miles a week...$10 to haul stuff and people isn't too bad...just a pizza or two!
My thoughts...keep it, drive it when needed, otherwise, get a couple mopeds, bicycles, hop on the bus, or walk...all good college activities!