Definately not crazy, but your "minimum" level depends on your willingness to scrape rocks. I'll caveat my experience by saying I've done it in a 13 footer once, at about 400 cfs but rising to about 1100 on the takeout day. If you're one of those who is absolutely stoked to hit "Lowdore" over and over again on a bad release year, then you'll be fine on the Salt as long as you have about 500+ and are willing to hop out and push your boat a bit. If you're one of those guys that busts into tears because you bumped a rock in Westwater, then you'll need 5000 cfs.
However, you might want to get a report later this season once the commercial companies get in there and start rafting it again. The flood this week has undoubtedly pushed the shoals around, may have altered rapids, and there may be a saguaro strainer or two, so my information is old.
Its a sweet river though. Probably my favorite short multiday that I've done. Really diverse canyon scenery and Sonoran desert is awesome. Have a great trip!
P.S. I found out the hard way that at low water the left slot at quartzite is too tight for a 13 footer, so don't even think about taking a 16 footer over there!