The primary factors that make Miller a logical trade chip are that: (1) if the Blazers are intent on bringing in a player worth trading for, it's likely to require sending out someone who is playing at Miller's level; and (2) I suspect Nate and Roy still have their heads in their butts where Miller is concerned. As much as Nate (and some say KP) overvalue Blake, if they also have high regards for Bayless I could see them having no qualms in trading Miller.
In my ideal scenario, our starting backcourt for the rest of this season, and possibly all, or part of next season will be Andre Miller and Brandon Roy. In spite of Nate and Brandon's pig headedness, I think now that Andre and Brandon have had a chance to start together and play significant minutes, they have seen that Andre isn't such a bad fit after all. Prior to his injury, Brandon was playing at a much higher level with Miller starting at PG than he was when Blake was starting and getting >30MPG.
I would like to see Bayless to get 25 - 30 MPG backing up both guard positions. Bayless is still inconsistent (great one game, awful the next), but he has shown flashes of being able to play effectively when paired with with either Brandon or Andre. He can be our instant offense off the bench guy and bring energy and attack the defense like he did in the 4th quarter yesterday. As long as he's getting consistent minutes, I think he would be happy in that role and it will help him grow his game until he is ready to be our starting PG.
At that point, Bayless could slide into the starting PG role and 35-year old Andre can either move to back up PG, or the team can decline his 3rd year option.
Given all the injury issues I have no problem keeping Blake around as insurance, playing spot minutes off the bench, or a bigger role if one of our other guards gets injured. However, with the way Miller and Bayless are playing, I would have absolutely no problem trading Blake.
I actually see Rudy as the odd man out. He's definitely got some talent, but with Brandon Roy playing in front of him and Jerryd Bayless capable of playing the back-up SG spot, I just don't see much of a future for Rudy in Portland. Now that he's back from his injury, I'd be dangling him as trade bait. I also think he's much better suited to an up tempo game and would thrive in a faster paced system (Phoenix, New York, Toronto, Golden State, etc.).
Although I don't think Patty Mills will ever be a good NBA point guard, I do think he has the potential to be an instant offense off the bench guy. Since he's on a cheap rooike minimum salary contract I'd keep him around, especially if Blake is traded. He can be our insurance 3rd string PG behind Miller and Bayless. And eventually, he could possibly grow into the instant offense off the bench role I see Bayless filling short to midterm.
So, of our guards, I see Blake and Rudy as the most expendable trade bait with the minum impact on both the short term AND long term success of this team.
BNM
Miller isn't perfect, and he's less effective at doing what Roy does than Roy is, but he's been the best PG on the team since the day he was signed. I said before the season that if Nate didn't start Miller and Greg I'd shoot myself. Well, I'm still here, but I did lose a lot of hair waiting for Nate and Roy to pull their heads out of their butts. The claim that Roy can't play with Miller was stupid. There is a difference between "can't" and "won't." 
