Are fairings allowed on the tour? Doesn't say on their rules page. I think the most aero savings will come from position on the bike (provided one could be uncomfortable for so long and not get injured), also things like dropper posts, fast rolling tires. Like you said most people focus on weight and imo forget there are 100 other things to optimize.
Fairings are allowed, if not deployable as a sail, because there is no rule against them and it aligns with the main rule which is you have to go the whole way using just your feet to propel you. That could change if someone wins on a fully streamlined bike and the other racers complain, though.
Position on an upright bike, tires, and other optimizations amount to very little compared to having your body and gear inside a streamlined shell. People who haven't experienced riding a streamlined bike or haven't been dropped hard by one just have very little idea how much of a difference it makes.
The other important advantage riding a fully streamlined recumbent in the TD would confer is weather resistence! The fairings keep that cold air off of you in the morinng/night, provide shade during the day, and keep you dry in the rain (you get wet from sweat though.) When the main challenge is mental those things are going to go a long way, especially on top of the comfort of not riding a wedgie.
Again with regard to weight and rolling resistence, my velomobile is a tourer that weighs 65lbs empty, has three 50 mm puncture resistant touring/city tires (Conti Contact Urbans), two which are little 406 BMX wheels, doesn't have a fairing covering my head/helmet, and I'm a paunchy middle aged guy who loves junk food, not a racer, and I'm always high as a mofo yet I can easily pedal up to 42+ mph on flat road. I could go faster if I had taller gearing than 53x11x50-559 since the cadence starts getting high at those speeds.
The record at Battle Mountain for a commercial velomobile (Milan SL, 3 wheels, 55-60 lbs) is 58.2 mph, by a regular middle aged guy who rides a lot commuting, not even an amateur racer. This year a 69 year old hit 56.9 mph on a different commercially available trike. Good luck finding a position and tires on an upright bike that lets you pedal up to that speed. Of course the top speed record is 89.59 mph (EIGHTY NINE) on a highly optimized 55 lb bike piloted by a very strong rider (Todd Reichert, who also won the Sikorsky prize for human powered helicopter and has a PhD in aerodynamic engineering).
I think there is enough flat/downhill/rolling terrain (and road) on the TD for it to make a big difference. The rides I do have much more vertical per mile and my average speeds have gone way up since ditching the unfaired bike even if I'm a bit slower on the big climbs from the extra 40 lbs.