I guess I'm decidedly in the minority. My answer to the OP's question is non-specific: "As many as I can afford." I miss Kodachrome. The last Kodachrome I shot was a couple rolls I burned through so it would reach Dwayne's before they shut down processing -- when was that? December, 2010? So, yeah, that's the last time I shot Kodachrome. It wasn't too long after that, that I shot my last rolls of Kodak slide film -- Elite Chrome 100, which BTW I thought was brilliant stuff. But it's all water under the bridge now, since Kodak doesn't produce any slide film anymore. So it's all Velvia and Provia now.
Look, the main reason why I would like to see Kodachrome to still exist is simple. It is still the best, most stable medium in existence for recording images. Unlike digital, it requires no backup schemes, and people 100 years from now won't have to resurrect obsolete computer systems in order to access the original files -- assuming they haven't been corrupted on whatever storage medium was chosen. No, the great thing about Kodachromes is that you can hold them in your hand and you can hold them up to a light source and view the images, needing nothing more to do so than your good ol' Mark 1 eyeball. And, assuming they've been stored with some semblance of care, what you'll see will look just as good as it did the days the images were taken. There's something magical about that, which is the big reason why it should still be around.
It seems at least plausible to me that, if Kodachrome were still produced in small batches, and marketed as being the best medium in existence for color archival work, then it might gain some traction in the marketplace. There will always be a need for a color medium that can survive the vagaries of time with a minimum of fuss and upkeep, or so it seems to me.
On a personal note, my main computer recently suffered a catastrophic hard drive crash, and it had probably been a month or two since my last backup. So of the approximately 800 gigabytes of image files I had stored on it, I probably lost 10-20%. It could have been much worse, but I have only myself to blame. Nonetheless, that's somewhere around 80-160 gigs of images that are just -- gone. This is one big reason why just about anything that I'm shooting these days that is important to me, I'm shooting with film. If a superior amount of resolution is required, I shoot with one of my medium format cameras, otherwise I'll use 35mm, which can still provide excellent images with the right film and technique. But when I'm doing one of my important shoots, it sure would be nice if I had Kodachrome as a choice.