I just solved this issue on my machine, and I guess people would like to know how.
I read a bit about Unity crashing issues in general, and I read that certain very old fonts could cause Unity crashes, and this led me to look in my user font library, only to see this:
Andrews-iMac:FontCollections andrewmcgregor$ ls -l
total 136
-rw-------+ 1 andrewmcgregor staff 1341 18 Oct 2004 Chinese.collection
-rw-------+ 1 andrewmcgregor staff 899 18 Oct 2004 Classic.collection
-rwx------+ 1 andrewmcgregor staff 2380 26 Jul 2012 Fixed Width.collection
-rw-------+ 1 andrewmcgregor staff 872 18 Oct 2004 Fun.collection
-rw-------+ 1 andrewmcgregor staff 2477 18 Oct 2004 Japanese.collection
-rw-------+ 1 andrewmcgregor staff 1217 18 Oct 2004 Korean.collection
-rw-------+ 1 andrewmcgregor staff 815 18 Oct 2004 Modern.collection
-rw-------+ 1 andrewmcgregor staff 856 18 Oct 2004 PDF.collection
-rw-------+ 1 andrewmcgregor staff 1164 18 Oct 2004 Web.collection
-rw-rw----+ 1 andrewmcgregor staff 23606 3 Dec 2007 Windows Office Compatible.collection
-rw-------+ 1 andrewmcgregor staff 1492 7 Dec 2007 com.apple.Favorites.collection
-rw-------+ 1 andrewmcgregor staff 2969 14 Jul 2011 com.apple.Recents.collection
Now, that looks a bit suspicious... those are the fonts from Microsoft Office way back when, since my OS install has been upgraded and ported to different machines since about 2003.
So I deleted them, and a bunch of similarly old fonts here:
Andrews-iMac:Fonts andrewmcgregor$ ls -l
total 1792
-rwxr-xr-x@ 1 andrewmcgregor staff 0 8 Apr 2004 Brush Script
-rw-r--r--+ 1 andrewmcgregor staff 36284 17 Feb 2005 FTL_____.TTF
-rw-r--r--+ 1 andrewmcgregor staff 35968 17 Feb 2005 FT______.TTF
-rwx------+ 1 andrewmcgregor staff 41416 20 Oct 2004 OptimusPrinceps.ttf
-rwx------+ 1 andrewmcgregor staff 57296 20 Oct 2004 OptimusPrincepsSemiBold.ttf
-rw-r--r--+ 1 andrewmcgregor staff 65932 25 Apr 2005 Vera.ttf
-rw-r--r--+ 1 andrewmcgregor staff 63208 25 Apr 2005 VeraBI.ttf
-rw-r--r--+ 1 andrewmcgregor staff 58716 25 Apr 2005 VeraBd.ttf
-rw-r--r--+ 1 andrewmcgregor staff 63684 25 Apr 2005 VeraIt.ttf
-rw-r--r--+ 1 andrewmcgregor staff 55032 25 Apr 2005 VeraMoBI.ttf
-rw-r--r--+ 1 andrewmcgregor staff 49052 25 Apr 2005 VeraMoBd.ttf
-rw-r--r--+ 1 andrewmcgregor staff 54508 25 Apr 2005 VeraMoIt.ttf
-rw-r--r--+ 1 andrewmcgregor staff 49224 25 Apr 2005 VeraMono.ttf
-rw-r--r--+ 1 andrewmcgregor staff 60280 25 Apr 2005 VeraSe.ttf
-rw-r--r--+ 1 andrewmcgregor staff 58736 25 Apr 2005 VeraSeBd.ttf
-rw-r--r--+ 1 andrewmcgregor staff 4268 9 Apr 2012 encodings.dir
-rw-r--r--+ 1 andrewmcgregor staff 5523 9 Apr 2012 fonts.dir
-rw-r--r--+ 1 andrewmcgregor staff 810 9 Apr 2012 fonts.list
-rw-r--r--+ 1 andrewmcgregor staff 5523 9 Apr 2012 fonts.scale
-rw-r--r--+ 1 andrewmcgregor staff 51220 25 Apr 2005 opens___.ttf
Lo and behold, KSP is now stable, whereas before I did that it would crash instantly on trying to launch.