How many d10, d20, ... directories are there? If there are only 10 of them, i.e. d10 - d90, I wouldn't bother with the d1/d2 level.

Keep in mind that you should try and keep the full path names short, because the Solaris DNLC (directory name lookup cache) only records path names of 32 characters or less... or at least that was the case last time I did a performance management course, on Solaris 8. Maybe (hopefully!) it has been increased in 9 or 10.