I have owned a Canon t3i with the 18-55 lens for almost 2 years now, but have never upgraded due to financial reasons, however I am looking to buy more lenses and a Camera body. Honestly, I don't really care about the 18-55 because I will be selling that with my T3i to one of my friends' who is wanting to get into SLR's. I am looking at either the 7D or the 6D. Granted, I know that 7D is an APS-C with higher fps, and the body is built better with aluminum. The 6D is a full frame with much better low light high ISO performance, but is also almost $900-$1000 more expensive considering that a used 7D is around $700-$800.
Also, if I go the 6D route, obviously I will buy 3-4 lenses that are used with the 6D or 3-4 lenses with the 7D.
Here is what I shoot: Landscape, wildlife, light trails, sunrises and sunsets (not directly but when the sun is rising/setting behind buildings, the city, et cetera). I definitely plan on getting into Macro photography this year, and would love to do some Star Trails also.
The Cameras I have taken a look at are:
70D (However I do stills, and not video and the ISO is better than the 7D, but not as good as the 6D, but I am wondering if that would be another camera to consider)
5D Mark II (Granted the 6D is better/newer and can be found for around just a few hundred dollars more when there are specials on it)
I have also took a look at the 5D Mark III, but sadly the price is far out of my reach.
As a final note, I am not concerned with Wifi or GPS.
Let me know what you think about what camera body I should go with.
I've yet to use Wi-Fi, haven't felt the need, so I can relate to you there.
You don't mention outdoors sports, or wanting to use long telephoto lenses outdoors to do bird photography...so I honestly must recommend the 6D, hands down. I bought mine a year ago, and I love it to death. The body is mostly magnesium and aluminum, with some plastic. It feels extremely rigid, my hands love holding it, no matter how big or small the lens is that's mounted.
I had a 50D for 4 years before this (put over 25,000 cycles on the shutter). Its body felt rigid, but yet less rigid, and far less pleasing to hold, than the 6D's. I've tried the 70D, 7D, 60D, Rebels, besides various 1 and 5 series bodies. I hated the 60D's and 7D's ergonomics and shutter button feel. I had planned on keeping the 50D a while longer, but it took maybe about 5 days to decide there was no need (I suspected I might feel this way immediately, but it took that long to completely decide). Sold it for a great price too. Hated to see it go, I loved that camera a lot as well. It was radically better than the Rebel Xsi I had before it. The T3i though, as Rebels go, is one of the best ones ever for its price. The 70D feels very close to the 6D's ergonomics. I think I like it. Really your choice should be between the 70D, and the 6D. I do hate flip screens, though, but most people love them if they spend much time shooting video with the camera. But a flip screen could work well for macro photography, though...and that is one of your use scenarios.
As for the cost of the lenses...that is just the price you have to pay. I suggest buying a used 6D if you can get one for under $1280 or so, assuming it's very clean and not beat up, scratched, or been dropped, etc (might not be easy). And maybe consider a new Sigma Art 35mm f/1.4 lens for your star trails and landscape photography. It would also cover most general people portraiture. Barring this, certainly the 24-105L can also be a very good lens for your use scenario...although at 24mm it has severe barrel distortion (like over 5%). It's mostly gone by 30mm though.
Fyi, I'm trying to sell my Sigma 24mm f/1.8, a fantastic lens for the money, and is brand new condition. It has about the lowest barrel distortion of any 24mm lens (other than perhaps the 24mm TS-E). 24mm is equal to 15mm on your Rebel. I wouldn't hesitate to use it for architectural and real estate photography...except there's not enough demand for it in my area. It works great for night sky photography if you close it down a bit...or if there are no stars or other points of light in the periphery...it can work well wide open (such as on a cloudy moonlit night in the wilderness). You can have it for about $300 less than I paid for my 24-105L.
Back to the 6D. It simply has the best overall (photo) image quality of any Canon camera. Compared to the view you see through the viewfinder of your T3i, it's like comparing a 30 inch tv to a 60 inch! The 1DX is very close in image quality to the 6D, the 5D3 somewhat close...and certainly the 1DX outshines them all at high ISO (as it should!). The reasons to buy the 1 or 5 series over a 6D, are the pro functionality and ergonomics, the autofocus, the speed, the features, the memory cards, the weather sealing...the larger viewfinders...the bragging rights. None of these is a small thing...but it really is mostly the autofocus!
The 5D3 really delivers the best of all worlds when price is considered (just over half the price of the 1DX), besides being able to shoot pro video with "magic lantern" hacks. If you ever are thinking of being a pro location or event shooter (with flashgun or strobes), and need to do pro quality video, the 5D3 is without a doubt the camera to buy. Also if you do pro quality bird photography with big expensive glass, the 5D3 is really the minimum body you should use for that. Better would be the 1DX (except for the loud shutter that can scare the wildlife)...and best of all will likely be the upcoming high megapixel full frame body (other than frames per second, it won't be fast, but it will surely have better image quality than everything in 135 format...possibly even the Nikon D800 at low ISO).
As for the 6D's autofocus, it sounds like your use scenario would not remotely tax it. It is VERY far from a great autofocus, the 7D's is slightly a bit better overall...but the image quality of the 7D, just cannot compare. Like comparing a $200 paint job done in an alley, to a factory Maranello job. The 70D's image quality is not very close to the 6D, but it's a bit better than the 7D.