saltpinch, I sold a DPMS after I ordered the 17. I knew that it would collect a LOT of dust in the safe before it saw any daylight again. The FN promotion was a nice bonus as well.
There are a crud-ton of little fine tuning items for it.
Grips, QD points, slings, spare items, particular decent ammo for the used casings, BUIS adjustment/directions, solvent, lubes, cleaning without being to OCD/abrasive, forend mods(2015), Stryker lowers for 308pmags (if already collected), triggers and then glass or magnified optics.
Try not to waste too much money yet and read as much as you can.
The forum has plenty of really slick owners with really nice mods for weight, speed, or casual benchrest days.