The way I understand the math, all of your recently-submitted shares are considered, no matter which worker they were submitted through -- so running several workers on one worker account or several should make no difference to the amount of reward you get when the block is solved. Even if one machine drops out... since the shares are considered collectively, it doesn't matter which account they were submitted through. They will age just like every other share you submit. (Correct me if I'm wrong, slush.) In other words, the older shares you submitted from the still-active machines have aged and become worthless too, you just can't tell because they are submitting enough new shares to keep the reward up.
This is interesting, in that case there still is the clear advantage of being able to quickly switch to a different pool in case that the current one goes offline for whatever reason.
Now, having said that, my proxy doesn't "dynamically associate a worker account to each machine." You still need to set up worker accounts in my proxy script. The difference is that you can assign those worker accounts to more than one pool. (Although you could probably hack it to do what you want. )
Ah I think you misunderstood me there, sorry if I was not clear enough. I ment to say that the alternative to what I said was your software; I understood the purpose of your software correctly.