Well, thanks for the ideas, guys.
If I had a buyer for the uni, or I didn't like it, or if I really had $8K, you're right, I'd just buy another boat, one with a carbon mast. But I have my uni, & I love it, I'd just love it more if I had a carbon mast (and a new mainsail). It's a long way from $3K for a mast to $8K for a boat.

As for carbon vs aluminum at Nationals. I'd love for someone to publish results of all the 5.5 uni Nationals, showing carbon vs aluminum. The only two 5.5 uni Nationals I have firsthand knowledge of :
1996 - two boats, both aluminum.
2001 - 6 boats, 3 Al, 3 carbon. Until equipment problems on one of the carbon unis, it was carbon in places 1st-2nd-3rd, and aluminum was 4th-5th-6th.

From online results :
2002 - 11 boats, based on names, I would say at least top 5 were carbon.