I used the same Elcan C79 for 4 years, and the abuse that it stood up to was amazing. On top of that, it's s__t simple to zero. However, am NOT a C79 fan. My biggest problem is that it is too bulky.
The Spector is a great sight, in concept. The 1-4X flip would be great, if it worked, but it doesn't. A number of the sights have alignment problems, namely, if you zero on 4X, your POI at 1X is about 4.5" high & left. Apparently the new ones have sorted out that problem, but I haven't shot them. Another consideration for the Spector, is that apparently the BDC in it was designed to corespond with a 14.5" barrel. no big deal at close ranges, but you need to spend some time on the range to figure out where your rounds will land at 400-500 metres.
The Aimpoint is a great CQB sight, and the 3X magnifier is a good idea too. But when you have both on your rifle, they're not only heavier than the C79, they take up way more room. Also, if you have your 3X magnifier stuffed in your kit somewhere, when the time comes to shoot somebody 300 metres away, you start shooting with the 1X, and don't bother to pull the magnifier out.
The Acog/Dr optic combo is probably your best bet, but also has some drawbacks. you definitely need to get used to barrel-sight relationship when using the Dr, because even zeroed for 50m, your POI at 10 metres (across the inside of a compund) is still 2-3" below your POA.
For no light the answers easy, PEQ2/PEQ4. But for low light,and civilian use, I suggest a good laser sight. YES I said it, a laser sight. Trust me on this one, they work.
That's all I've got.