I haven't been able to substantiate the difference between 1:100 and 1:50 during normal agitation. You do run the risk of exhausting your developer at 1:100 though and have to make sure to put plenty in there.
If you decide to use less agitation, say every three minutes, or every five minutes, or even just agitate once or twice during the entire developing cycle, 1:100 or even 1:200 becomes advantageous.
Jokingly, you will use twice the developer at 1:50... BUT, less of your time. And Rodinal is so cheap to use, I'd just go 1:50 all the time like I did when I got sick of agitating for 18 minutes.
I would use the same dilution for 35mm as 120, perhaps just a smidgeon less due to the heavier base of 35mm. I don't think it'll matter much.