Are you stuck with US? Who else flies your routes? CO and DL would seem to be good alternatives. You could probably fly to CP with $8000, $72 a segment with the 7.5% tax.

It's really not worth it as I know that lower levels have been upgraded before me as a CP and I have not been able to use all my TA vouchers in the past. With GoEnvoy and a $1200 upgrade minimum for miles and vouchers, paid C class or purchasing an upgrade with GoEnvoy is the way to go. I heard of someone who flew paid Bus Elite on DL for around $1200 recently. You could barter your US miles for UA SWU's etc.

If you are ingtent on staying with US the status challenge for $600 would be the way to go, although as CP you should get it for free IMHO. I had my first shuttle flight with Delta last Monday. I miss US and the great folks on the shuttle but management is making this one a no brainer. *A is what I will miss.