Aftermarket parts
FAL triggers are not that great.
I used an FSE trigger set in one of my FALs. It's very nice. The other has an Austrian STG trigger, but I used a Falcon Arms trigger improvement spring kit in it. There are some other tricks to make the FAL trigger better. It's very easy to work with.
The sights are fair at best.
I don't like how the front sight and rear sight are on different halves of the rifle, but DSA has a few major improvements to the rear sight. One simple fix is a hooded sight with a smaller aperture. Much better. My other FAL has a "Hampton" lower receiver which uses an integral AR15/M16A2 rear sight assembly. That opens up a whole world of rear aperture options as well as much better elevation and windage adjustments.
The FAL also seems to be nose-heavy to me, with poor balance.
A shorter barrel helps that a lot. I shortened one of mine to 18", the othet to 17" + a 1.5" muzzle brake. Some FALs have bigger heavier flash hiders.
It isn't a particularly easy gun to scope either
That used to be true, but isn't any longer. There are a few different railed top covers that fit tightly and work well. Both my FALs have quality railed top covers that never need to be removed (even on the Para!). I installed these mounts when the rifles were assembled and never removed them. They stay tight, hold a zero, and have never come loose. Scoping my FALs is as easy as scoping an AR15. In fact, if you look at my top FAL (the Green Machine), it's using an Armalite AR15 scope mount.
Accuracy is ok, but nothing to write home about.
I agree with you there. The FAL isn't a tack driver. FALs are notorious for first round flyers and handguards putting pressure on the barrel as it heats up. With open sights, there could be play between the two receiver halves. If you want an exceptionally accurate semiauto, the AR10 platform is a much better choice, maybe even the PTR91.
The basic military spec FAL might need some tweaks before it's satisfactory to some US owners. But keep in mind that sometimes we are trying to use old military rifles in ways that they were never designed to be used. The FAL was a front line service rifle, first fielded in the 1950s and intended to be used like the AK. It's an older design than even the M1A/M14. It wasn't designed to be a target rifle, or used with optics, or for precision work. However, it is somewhat improvable if you have some mechanical ability and do your homework. I consider the FAL to be in the same class as the AK (but in a larger caliber) and the Galil. If that's not your thing, there are many other good rifles to choose from: AR10, M1A, M1 Garand, PTR 91, etc...