Interestingly, looking at Australia's teams between 1989 and 2006/07, there were a handful of occasions (1991 and 1996/97 IIRR) where they went into Tests with three specialist bowlers, as they had the likes of Mark Waugh, Stephen Waugh, Allan Border, Michael Bevan, Greg Blewett, etc. who could offer not-completely-count-out-worthy options. They've the same thing currently with Symonds, Clarke, Katich and even Hussey isn't the worst.
So given Katich really, really is just bashing on the door currently, and is a superb player of spin, and is one of three decent part-time spinners available, why not just pick three seamers? Go in with
Jaques
Hayden
Ponting
Clarke
Hussey
Katich
Symonds
Haddin
Lee
Johnson
Clark
Which gives astoundingly deep batting and hardly weakens the bowling considerably as even in the seam department there isn't exactly a whole host of people banging down the door - witness one-season wonders like Bollinger being picked in squads and three-game semi-wonders like Casson getting into teams.
If you can pile-up massive totals, which that batting-line-up should do often (even though it does have Symonds in it) then even with a bit-part attack you can still cause huge problems simply by pressure of runs.