I don't shoot LF, although I own a 4x5 or two. So I can't really comment on contact prints. However, when comparing enlargements from 35 mm (Nikon in my case) vs 6x7 (Pentax), and 6x4.5 (Mamiya) in between, the one thing I think is clearly different is the effect of accutance, which is related to developer, dilution and agitation. The accutance "margin" for 35 mm is enlarged more, which gives it the appearance of an image that was sharpened in Photoshop with a larger radius. Depending on the lighting and subject, this can be a good or bad thing. For me it partly explains why the tonality in larger negatives is handled more gracefully in a print. I agree that the taking lens and enlarging lens are both important factors, but I think they tend to outresolve the accutance effect, so the effect will mostly be visible despite using good rather than exceptional lenses. With that said, I am not afraid to print 35 mm negatives to 12x16, and if I could print larger, I probably would. With that being true for 35 mm, all the more so for every step up to 6x4.5 and 6x7 and beyond. In any event, I couldn't afford anything but 35 mm until about four or five years ago. One of the joys of larger prints is that one doesn't have to stand with your nose to them in order to take in what they have to offer. With wall space at a premium, one can display them slightly out of reach and they can still be appreciated. To turn it around a bit, one should be excited about what is possible from 35 mm, to the effect that it is absolutely worth using for a very wide range of purposes.
It is just as important to be able to afford your equipment, get it to where your subject is, to have it respond in the way you need to capture the image, and to be geared to process afterwards. That is my main reason for not shooting LF, but I can see why others would want to. However, I believe that few LF shooters extract the inherent differences between LF and MF in a way that matters, yet there is no lack of pretentiousness. One can easily apply the same logic to MF vs 35 mm (or digital sensor sizes!). If you just happen to love owning and shooting large cameras, my comment is not aimed at you, but rather at the crowd who endlessly obsess over the most minor of perceivable differences, and who look down at lesser formats disdainfully, while creating nothing with the larger format to really set them apart. One finds this mentality in so many other walks of life as well: fishing tackle, running shoes, golf clubs, cars, make-up, knives and guns, musical instruments - the list goes on and on. I walk into our local fishing-tackle retailer, and see guys buying fishing rods and reels costing well over a thousand dollars, and they probably don't ever catch a single fish with them. There are people armed to the hilt, with nothing to shoot (thank goodness). Then I wonder why we need gear and stuff to define our identity. Creative content will almost always triumph over absolute image quality, as long as the image quality gets above a certain bar. How high that bar is depends a lot on subject and context, which is why there is a place for larger formats in the first place. And nothing should discourage us from having fun, of course.