Does analogue summing make a difference? If it's a good analogue summing unit, then yes.
Is that difference beneficial? Well that's personal taste and choice isn't it?
It's really down to how much easier the analogue summing makes your job as a mixer, and that varies depending on the mixer. It's also down to budget, you're not going to spend thousands on an analogue summing solution in a non-profit studio situation and think that was a real benefit.
Personally I think that a great analogue mix bus chain of compressor and EQ will make far more difference than analogue summing. However high end analogue summing is another tool, it does something else that cannot be achieved by anything else.
I bought an X-Rack summing unit because I loved mixing on SSL desks where I found it easier to achieve my mix goals when simply putting up levels. It was a final piece of a puzzle for me, and I already had a lot of outboard gear that I had built up over years covering other areas. I also wanted a "clean" summing unit as I had plenty of other gear for adding character.
In the first few weeks I spent a lot of time doing controlled summing tests to really see what it was doing. My studio is based in one of the top mastering facilities, so I would also do blind testing with the mastering engineers in their room on various monitors (big PMCs etc).
More depth, punch, bass extension / phase alignment and a smoothing of the brittle digital top are a few things that were very obvious to our ears.
In reality it's a small difference when compared to the other pieces of gear I've purchased, but it allows me to get to the goal quicker, and after working with it allows you to achieve higher quality mixes than was possible before. Not by much, but at that level every little advantage helps
Is it necessary? No.
Will it be right for everyone? No.