The Trek 500 will probably have friction shifting and 12 speeds. A new bike will have indexed shifting and more gears. And probably a warranty, too.
The 1985 500 is a mid-range series with a Reynolds 501 frame, double-butted chrome-moly steel; decent stuff, maybe better than decent.
OTOH, the 500 might be a racing bike which may be uncomfortable for commuting, although perhaps not uncomfortable for 10 miles. One consideration WRT racing bikes is that it might be difficult to install a standard rack - but it IS eminently possible to get a seatpost rack. A rack may be important to you to carry a day's needs.
On yet another hand, you may really like the 500 and find yourself spending long hours riding it on weekends, or whenever you days off are.
If it fits, and if you like biking, the 500 might be a good choice. The Trek FX1 is low-end today, but it's probably a LOT better than the low-end in 1985. Given the winds faced in flat lands, though, I, too, recommend looking at something with dropped bars.
I'm another one who rides an old bike, but I can do almost all of the necessary work myself.
Last edited by philbob57; 06-05-19 at 04:17 PM.