Re: How important is it for tennis that Soderling beats Nadal tomorrow?
I highly doubt you are going to get an objective opinion to your question here, thought I doubt you want one.
For the rivalry between them, if there is one, then yes a Rafa win might put it to bed, but then again a player like Soderling will always have a chance to trouble Nadal if he can stay consistent, but it might have lost some of its buzz.
Better for tennis? All depends who you ask. For an average tennis fan it is probably important for Nadal to win, they want to see a Federer - Nadal final, or at least a Nadal - Murray semifinal, that goes double for the fans at Wimbledon. For this board, the majority will want a Soderling win as they see him or Murray as an easier opponent for Federer and dislike Nadal. Personally, I don't think it matters all that much, at least not in comparison to Federer's matches. I'm sure if he failed to make the final then viewership would drop significantly, especially if Rafa did too.