I would agree with the above. If you are really worried about cost, do slaves. I personally am in the "former" camp. Although, not for the listed reason.
I had some "slave" switches in my last house. I ended up selling them before I put in all the US2-40's in the new house. The reason, in my last house I used slaves, then wanted to change the faceplate to add functionality...and unfortunately it ended up being AT the slave switch.
In my new house, I've not had to re-wire anything, and I've already swapped around a few switches, or added features.
In my kitchen, I have a main switch, and a switch for the lights over the sink. By changing the faceplate + links, I was able to make a DUAL 3 way out of it. Each switch can control either lights. Well, it was easier to say:
Main switch:
left side controls the main lights (on)/all lights off
right side controls the sink
Sink sw:
left side controls ALL the lights (on/off)
right side control the sink.
It was something my wife and I discussed, so it ended up a bit complicated but suits us.
Another example (as that one was a bit poor, but was trying to get my point across):
we have a 3 way that controls the entertainment room. Since we do not use the "salve" switch in the loft to turn lights on, I was able to (by links) re-purpose that switch as a 4way to the living room. The reason, by leaving the living room on, you can get enough light to go up the stairs to the top floor without turning on the stairwell lights. This has the benefit of NOT waking up my children by us needing to turn on the hallway to get to the master bedroom. So, the loft's slave was in the hallway, and I just made that become the 4-way to the entertainment room.
Also, was thinking of adding some Audio controls for my whole house audio, like how a user did on Homeseer's website. Basically certain links will activate events that control audio. I could put those on ANY switch in my house. Which for that loft switch, might be a good idea (make the faceplate a top/rocker and 4 buttons on the bottom). The rocker is the light, the bottom is the audio controls.
I hope that go my reasoning across. And really, for me, if I would have went slave switches (assuming I did not care about the benefits above), I would have saved 5 switches. So, whatever the cost difference is for a (Slave vs. a US2-40) x 5.
--Dan