Not sure how the miners handle this internally, but usually when people spend unconfirmed change and pay a regular or normal fee both TX get confirmed within the next or very few blocks.
Thanks for your info.
-snip-
is that even worth it?
For the miners? Sure, its not like we are anywhere close to the 1 MB blocksize limit, so there is enough room. Any TX that pays and gets confirmed is money in the wallet. There is no downside or at least I am not aware of one currently.
It is good for the general bitcoin users as well.
Say if someone send you 0.05 btc but for some reason didn't attach a 0.0001 fee, you may need to wait for a few days without luck, contact the sender, explain the problem, persuade and teach him to create a double-spend transaction with fee.
Or you could simply send that unconfirmed 0.05 btc to yourself with a 0.0001 fee to solve all the problem all by yourself.