You need to make a choice. Like you, I'm stuck in the netherworld between Silver and Gold. What hurts me is that based on the west coast, many of my miles will always be earned between SFO and HKG with half EQMs on NWW. In several years I have had one upgrade on Continental, but quite a few on NWA. In this day when the value of domestic First Class travel has decreased so much-it's now a larger seat, 2 free drinks and maybe a meal you would spend $15 for at the Olive Garden-I've come to the conclusion that I would rather fly a first class airline than in a first class seat.
As a Silver Elite with a PC membership I get most of the benefits of a first class ticket-priority check-in, security lines, boarding and baggage handling, along with lounge access in most airports. I view the extraordinary rare upgrades as icing on the cake. As you might tell from my sig, I'm very close to Gold this year so I will do a MR and end up just over the limit. At the same time, if I had not been able to get an extraordinarily inexpensive flight (i.e. $150 all in SFO-CLE-HPN on CO metal) I would remain Silver for 2007.

Good Luck!