Are you starting from zero miles or did you earn/fly some trips last year on USAirways? The buy up from zero to gold would be rather steep. Probably not worth it..............
The only trip worth a good upgrade in your list is the Costa Rica flight because it's flown (via CLT) on the 757-200 with International Envoy seats. The Saturday only flight from PHL is operated on an A320 with basic domestic seating.
The CLT-SJO 752 flight ends on March 24, 2012 and is replaced with a 320.