There have certainly been examples in recent years of a market's frequencies being shuffled to bring additional signals into town - in Boise, for instance, there's a plan in the works to shift several class C FMs up one notch on the dial to allow for another new signal. The company hoping to bring the new signal into town has to cover the expenses (both technical and promotional) of the stations being forced to shift.
But - and this is a big but - this is increasingly difficult to do. Any shift you make has to fit with spacing rules that take into account stations up to 0.6 MHz (3 channels) away and more than 200 miles distant. You can do that in Boise because there's very, very little else within 200 miles in most directions. In Vegas, though, you need to fit with signals in Arizona (including the surprisingly crowded Lake Havasu-Bullhead-Laughlin-Kingman market), St. George/Cedar City, and down the 15 corridor into California.
As noted earlier in the thread, you can't move KSNE to 106.7 because of KVGQ at 106.9. You can't move KVGQ to 107.1 because of the 107.1 in Havasu. You can't move 107.1 in Havasu to 107.3 because of KXTE. You can't move KXTE to 107.7 because of KVGS...and of course you can't move 107.9 anywhere.
And if you can't move KSNE to 106.7, you can't move KOAS to 105.9. (Which you can't do anyway because of a St. George signal at 106.1...)
Same deal lower down the dial - KLUC can't go to 98.7, in part because of the Highway Stations signal on 98.9 in Essex CA and in part because it would create an interference issue with KCEP 88.1. 99.3 can't go to 99.5 because of the Highway Stations signal on 99.7 Mountain Pass. KXNT-FM can't go to 100.3 because of 100.1 in Kingman and 100.1 in Crystal (out past Pahrump).