Should I proactively replace old GFCI outlets?
I think this depends on the quality of your old outlets.  A lot of times builders might use the lowest quality for outlets and I have gone through houses that were 10-15 years old and just spent a day replacing them all.  

However with GFCIs it is not very common for these to be cheaply made.  They would have to probably be quite a bit older than 10 years old to be junk GFCIs.  So I would keep them unless another GFCI in the same room fails.  I like my outlets to generally match if they are right next to each other but that is just aesthetic preference.  

Really though if you are talking about electricity in general (save for very old knob and tub or aluminum) if you touch it there is much more chance of you causing an issue than you preventing one.