My $0.02 ...and just remember, you asked for it... [:)]
I know you like the FNC - they're great guns, but they've got two big drawbacks for a shooter. First, parts are hard to find and expensive, and the supply isn't getting any better. Second, there's no versatility - you have one gun in one caliber only. With an M16, for example, you can have several different set-ups in different calibers; lots of versatility. The HK has the same problems, only worse with parts. Not that either an FNC or an HK is a bad gun - they're not - but I'd be worried about keeping them running in the long term, especially if you do a lot of shooting. The M16 may be inferior to both of them in several important respects, but parts are affordable, made in the US (so no parts importation problems), everything is user servicable, and the AR15/M16 has more versatility than just about any other weapon out there.
That said, I'd lose the FNC's. For what you'd get for the full auto FNC you could get a nice non-Colt M16. Take your $2500 cash along with another $4500 or so you'd get for the two semiauto FNC's and get a 1919 while you still can. If I were you, I'd keep the HK though. I assume the HK is a sear gun, so that sear can go a long way if you get other semiauto HKs in the future. You can swap the one sear/trigger pack between several different HK weapons and go full-auto in any of them.