The best way to spend your own money on First is to use OneWorld round the world tickets. I'm just about to start this itinerary (in parts spread over the next year) all in F (or J where there is no F):
MNL-HKG-JFK (all on CX)
JFK-SFO-DFW-ANC-DFW-SEA (on AA)
SEA-LHR-DXB-LHR (on BA)
LHR-HEL-CDG (on AY in J)
CDG-HKG-KIX-HKG-MNL (on CX)
That's 16 flights, totalling 44309 miles.
The cost including all taxes? US$9083.
That's worth it.