And on the other hand there are plenty of applications where you can assume that the encoded data doesn't need any pre-processing, either because your program w

And on the other hand there are plenty of applications where you can assume that the encoded data doesn't need any pre-processing, either because your program was the one that did the encoding or because validation occurs on a higher level (e.g. a cryptographic MAC). The cache issue is a good point, I wonder how dedicated your process has to be to processing base64 text for that to not be a factor.