To be honest that is your decision, but I have a 2015 Reserve- no THX or Sync 3 and I am not feeling left out or feel like I am missing anything, but that is just me. I have driven an MKC with the Sync 3 and THX and while it is nicer, it did not make my system seem any less. Now, apparently with the 2018 model there will be some design changes, do you buy now and if the updated design appeals to you; do you now jump to the 2018?
I would also check Bluebook on the car you mention, with a base Reserve and no added options noted~ I believe it might be priced a little higher than expected...