I doubt Chafee and Snowe can be primaried, but even if they could it's probably not the greatest idea since conservatives have a tough time winning election in both states, especially Lil Rhodie. The places to really spend the funds are the open seat in Minnesota and against both Nelsons (Florida & Nebraska). For more uphill seats to target there's the open Maryland seat as well as Conrad (ND), Stabenow (MI), and Cantwell (WA).
With all that and with the GOP seats that need to get defended, why on earth should Pubbies waste time and money on a totally unwinnable seat like Byrd's? Even against that commie up in Vermont and the NJ seat if Corzine retires would be better places to compete.
At this point, you're right. There are many other places the GOP should spend money. And they will. It is worth it to keep your eye on WV, though, and to make sure it's a credible race to the end. Because Byrd is not long for this world and his sanity will go even sooner.
The only thing keeping him elected is that he brings home the pork. If he's stopped from getting his pork projects approved, then he's of no more use to them, and the rationale for keeping him elected goes away