So another week and another idea in my head. Latest thought is to keep my A99 and just enjoy it and build up some glass for now. Just recently sold my Rokinon 14mm UWA so as of now all I have is my Sigma 50mm f/1.4 and my old Sigma 70-300 so an update to my glass is sorely need.
Harry brought to my attention a review Tom Bricker did on the Rokinon 12mm fisheye and we all know how much I loved my old Rokinon 8mm fisheye
Ive missed that lens ever since I sold it, was the sharpest lens and the picture quality and colors were great out of the lens. The part I miss the most is the manual focus believe it or not. Once you dialed in the focus (which took me a while to figure out being a newbie) you never have to touch the focus and is perfect for ride like Big Thunder where the ride vehicles are moving at an accelerate speed, say by by to an AF lens trying to grab focus going that quick. Lastly its a lens I can keep even if switching to the A7II(9) eventually, just throw on the cheaper adapter and off you go with no worry about AF.
The A99 is a great camera. I miss some things about it, though overall, I'm quite happy with the change.
You need to ask yourself what about your photography gear really needs to grow or change..
If it's simply a matter of wanting something smaller, than the A7 series might be your answer. But in terms of body, you are saving about a half pound with the A7ii. So only you can decide how meaningful the weight savings would be.
In terms of image quality... I can't explain it, but if you look at the dpreview comparisons between the A99 and the A7ii --- They look very very close. Considering my D750 using a cousin of the same sensor, it doesn't make sense to me. The D750 is noticeably better at the mid and high ISOs. So the A7ii should be noticeably better than the A99, but I don't see it, even when comparing raw files on dpreview.
Anyway, beyond size.. what's lacking. Would your experience improve more, would you get more enjoyment, out of better glass or a different camera body.
For me, the biggest shortcomings of the A99 were some gaps in the Sony lens lineup, the so-so ISO performance for full frame, and the mediocre system.
I still happily chose it over the D600 and the 6D, which has similarly mediocre AF systems, even if they had better lens lineups. The 6D has better ISO performance, but the D600 and A99 both had better dynamic range. And truthfully, when I bought the A99, I didn't quite fully feel the constrictions of the A-mount lens lineup.
When the D750 was released, it really answered my shortcomings with the A99 -- the best AF system of any camera, even better IQ than the A99, etc.
Still, within the A-mount world, there is some great glass, fairly affordable. I still truly love the Minolta 100/2.8 and 200/2.8. These are simply phenomenal lenses, much cheaper than "new" lenses, but optically nearly flawless. I never found an affordable ultrawide that I truly loved for Sony, but you might be on the right track with the new 12mm.
You're lucky to have a somewhat limited lens selection -- If you chose to change brands, you could do so without much pain.
Personally, my take:
The Nikon D750 is the best full frame camera currently out there in terms of traditional still photography. The Nikon lens lineup is superb, especially in terms of ultrawide. (the 14-24 is the gold standard but out of my size and price range. But even the affordable 18-35 is great optically). The camera is fairly small and light -- it weighs only 200 grams more than the A7ii. The IQ is second to none, among 24mp cameras. The AF is the best of any camera, period. The OVF is large and bright, and better for tracking action than EVF. 6.5 FPS is the fastest outside of the super expensive professional dSLRs.
The A7ii looks to be the best in terms of more compact full frame-mirrorless. There are strong arguments that mirrorless is better for video than traditional. Obviously, live view is much better than any traditional. And EVF has a lot of big advantages over OVF. While in theory, the IQ should be about the same as the D750, in every comparison I've seen (dpreview, imaging-resource, and DXO testing), the D750 looks noticeably better. The AF may be improved int he A7ii, but I suspect the D750 is still noticeably better. But these tradeoffs may be worthwhile for someone who wants smaller, who wants EVF, live view. You are gaining quite a bit.
Keeping the A99 is really the best option, if you have a limited budget and mostly want to improve your image quality and take different types of shots. That way, you can use your budget towards great glass. A truly good telephoto lens, macro lens, ultra wide -- these really open up different types of photography. There is nothing WRONG with the A99 image quality -- it's still better than any APS-C camera. Keep it below ISO 10,000 or so, and you are still doing great. It's still got the great EVF, great live view. What would you really be gaining by switching to the A7ii? A slight bit of IQ, a slightly smaller body.
And of course, the next few months will possibly bring a Canon 6dii or 5div, a Sony A9 or A99ii, etc. So there might be other options to consider as well.
Now for myself..... My wife is expecting a nice bonus and said she would buy me a lens. How do I break it to her, that the lens I "need" is $2,000...
versions of LR and CS6 on my computer for a while but went legit 
and signed up last year for CC
