My 'collection' is pretty pedestrian by THR standards, but I've got most of my major needs covered.
I don't know, compared to mine your's looks pretty sweet!
• Carry .45 (Kahr or Glock perhaps?)
I take it you are talking about a compact .45? My first question is, do you carry? Not much point in a compact if you don't need it for CCW.
• Second AR-15 (It is an election year, and I really like AR-15's.)
Eh. I'm not convinced we are looking at another AWB coming down the pike. Unless you are looking for an AR in a differenc caliber than the one you have, I'd put this pretty far down my "want list"
• Large caliber centerfire rifle (Seems like a hole in my collection. 700 SPS?)
Since you didn't say anything about hunting, I'm guessing you are looking for some sort of long range target rifle? Those can be lots of fun, but another question is do you have a range that supports shooting at 400-500 yards or more? Not a lot of them do.
• NFA stuff? (Suppressor for my Buckmark? SBS or SBR?)
This sounds like some "fun to have" stuff, if you are willing to put up with the (admittedly minimal) hassle of owning one.
• Progressive Reloader? (I'm not a high-volume shooter, but single-stage does get old sometimes)
You seem to have enough guns to justify it, assuming you do shoot enough to off set the start up cost.
• Ammo (I have ‘enough’ - a few hundred per caliber - but not as much as I really should)
I might get some more for your "main" calibers, but while you can never have too much ammo, you seem pretty well covered here.
Bottom line, if it was me I think I would go with a larger caliber centerfire rifle, a .44mag revolver, or the compact .45. They all fill "holes" in your collection and seem the most useful/usable choices.