As a used car, the 300C is getting more affordable every day. I've seen 2007 models for $21K.
I remember the gas crisis of 1973 when a fellow office friend bought a 2 year old used giant Caddie for about $3K. People were freaking out about gas prices and shortages and dumping their V8 sedans for anything that got good mileage.
If gas gets to $5 per gallon, I'm hoping to pick up a used 300C really cheap. Since I drive only about 6K miles per year, I really don't care much about mileage.
The truth is that it makes no sense to sell it off right now. Loss and cost of aquiring new vehicle may not recoup any gas savings. If you shop for new you may want for something more economical, but I do not see any practical reason one would have to rush to get rid of their 300Cs.
Gas prices are one of the reasons Lincoln decided not to put V8 into their upcoming MKS. MKS is a very nice car in my opinion, but lack of V8 option creates the feeling that something is missing. Though these perceptions may change over time.
However, I have got hooked to V8. It will be difficult to go back. I tried CTS with 3.6 DI which comes close, but still does not feel the same solid and strong as HEMI. MKS's V6 is not even as powerful as powerful as the one in CTS.