To answer the question whether you can just move the data from v3.71 to v2013 folder and convert, the answer is yes. I have done it twice now without issue. My reasoning is that why move all the crap (crystal, report tables, VI's etc) that you just have to delete anyway. The only thing of value might be the users but you have to modify security anyway, so why not start fresh. The only gotcha that may be an issue is if you have UDF's. But in Eric's situation, he had already performed the migration once so the data dictionaries reflected the UDF's.
I wonder if you can rebuild the data dictionaries to reflect the UDF tables somehow.
I create the data folders first in v5.0, then rename them. Then copy/paste the v3.71 APxxx, ARxxx, etc in place. Of course, get rid of the crap tables (tmp, old, etc) prior to the conversions.
For vanilla installs, go for it.