I use an R2 (not A) and an R3A. You're correct about the difference being the viewfinder magnification. This also means that the widest frame lines in the R3A is a 40mm set, and 35mm in the R2A. For what it's worth, the 40 framelines in the R3A are not visible to most people with glasses. With my close-fitting glasses and my eye pointed straight ahead, I can just barely sense the 40mm frame in the R3A. If I look over to see the frames, they disappear. If you want to go without glasses to see the whole frame, the R3A takes the Nikon F3A finder diopter lenses.
With the R2A and a 28mm, you might find that you can use the outer edge of the finder area as a finder for 28mm. However, Voigtlander makes a very nice 28mm auxiliary finder, and a combination 28/35mm mini finder, which I like a lot, and use on several cameras. Of course this runs up the price. Lately I've also taken to using the Cosina-Voigtlander 40mm auxilary finder on my Fuji GW690. It's much brighter and clearer than the built in finder, and you can see the details of what's happening in the frame much more easily.
I love the R3A finder at 1:1, and use a 75mm f:2.5 Cosina-Voigtlander a lot. I also have a couple of 40mm f:2 lenses that match the body nicely. For my 90's, the 1:1 finder is also much nicer than the .7 mag. The effective rangefinder baselength of the 1:1 finder is also a bit longer, useful if you plan to use fast lenses that require a little more focusing accuracy. I find that for street shooting and for sports, nothing beats a 1:1 finder, one of the reasons that the Leica M3 was preferred at .91x. Shooting with both eyes open allows you to feel like part of the environment, rather than observing from afar. It also allows you to see what's coming into the frame. I often pre-compose and wait for something out-of-frame to arrive in the shot. For sports, this is invaluable, and nice for street shooting as well.
I don't think you'd be unhappy with either. If you shoot a 35mm lens a lot, or are OK with estimating the 28mm field from the built-in finder, I'd say go for the R2A. If a bit more focusing accuracy would suit, or you use longer lenses frequently, and you're going to use an auxilary finder for the 28mm anyway, I'd go for the R3A.