As you've shown, Genuine Fractals creates a "grain" artifact as part of the fractal scaling method. This effectively disguises pixellation when doing oversize output of image files, but the grainy quality can be obnoxious with some images (as you point out in your sky detail). Of course, if the image is meant to be viewed at a distance, the grain isn't a big problem and it's far preferrable to obvious pixellation.
Does the Cat image detail really look good? Notice the obvious jaggies in the whiskers. To be sure, this is a 72 ppi image, not close the minimum resolution you need to keep pixels from showing up on an Epson photo printer, but I assure you that a good scan from film wouldn't show whisker jaggies at the same magnification. The other details in the image are lower in contrast and have much finer texture so the pixellation isn't as obvious.
Sorry, but I don't agree that digital is "there" when compared to 35mm. There's no substitute for real image resolution. A 2900 ppi scanner isn't getting all the detail that even an average quality film offers - 4000 ppi covers most film under average shooting conditions. Sharp images shot using fine grain film on a tripod sustain even higher resolution scans.
These aren't small resolution increments. A 4 megapixel camera provides 2240 x 1680 pixels to work with. A 2400 ppi scan provides 3400 x 2268pixels (7.7 megapixels) and a 4000 ppi scan provides 5668 x 3780 pixels (21.7 megapixels).
I'll put up a scan from a Provia F slide from my 2400 ppi Minolta scanner against a full res tiff image from my Coolpix 990 anytime. And a higher res scan will continue to hold its advantage when scaled with GF - better remains better.
The real test for someone shooting landscapes is how well fine details like leaves and branches hold up to enlargement. The acid test that most digital cameras and their lenses fail is capturing branches against a blue sky. Color fringing an poor detail are a problem with nearly all digital cameras for these kinds of images.
Yes, there are other excellent reasons to have a digital camera. I own one and use it. However, there's no contest between it and any of my 35mm cameras for enlargement potential. And since I never know when I'm going to create a shot worth a big print, I avoid using the Coolpix most of the time. The Coolpix is great for making immediate images that save time and money in my work.
My next investment in digital imaging technology will be a Coolscan 4000, not an incremental upgrade to my Coolpix. It will be a while yet before there's a digital camera that will lure me away from film for most of my shooting.