I bought a bog standard 13" rMBP two weeks ago, with the refresh yesterday should I exchange my macbook to get the slightly better processor and the 8gb (double the ram)
The problem is as its like 16 days old so I'm out of the 14 days and I was quite close to buying the model above this one.
If you paid full retail price for the 2013 base model (4/128), then yes I would at least try to exchange it for the new base model (8/128). It's basically 4GB of extra ram for free.
If you got the 4/128 on discount or sale of some sort, then I would keep what you have and be happy. I have the 4/128 and it's great.