35 is so near to 50, that they can be exchanged as a "normal" lens - it just depends on how one is used to look at things.
IMO, the set 35/50/85 does not make much sense from the focal length spacing. 28 (or 24)/50/85 is much better (though I would prefer 105 over 85...). Alternative: sell 50, get 20/35/85 (20 as "true WA", 35 as "wide normal", 85 as "tele" - comes close to what kind of kit one would put on a Leica M, anyway).
I agree about the 28/2.8 Ai-S. Excellent lens, though at times not wide enough. However, served me well as my only WA for a couple of years. Later, I got by without a 50 for years - just 20-35 and 80-200, neither missing nor using that 50 much.
It depends on which meaning you want to give your wide angle lens, and how important the 50 "normal" field of view is for you. Wanna keep the 50 for it's FOV, you need a wide companion - get the 28 or 24 (or even 20, that's what I probably would do nowadays). Wanna get the 35 - sell 50, get something even wider, too.