Here in Oz, most of the 2013-2016 V-twin Spyder owners that I know wouldn't part with them for anything, but it does seem that there are fewer ST's than there were RSS or RT's - maybe it was a 'Sporty or full-on Touring' thing, and the ST's just didn't really fit into either camp.
However, I don't really think you need to buy
ANY OEM parts up front, except maybe a replacement belt if you plan on riding more than the average number of dirt/gravel roads (ie, half or more if your riding), or intend keeping your Spyder until it falls apart at some stage in the far distant future. Mind you, I do the former and still intend doing the latter on the 2013 RT Ltd that I purchased brand new over a decade ago, averaging more miles a year than many Spyder riders do in a lifetime, and I haven't needed a new OEM
ANYTHING yet, altho now that the milage is getting well up in the 6 figure range, I am
juuuust beginning to see some wear signs on the belt...
Do the usual 'due diligence' checks, then if all is good and it's in pretty good nick, well maintained, and at a reasonable price...
Just Buy the Damn Bike, you Know you want to!
Then...
Ride More, Worry Less! 