Over at the OpenBOR forums I found download links for most PAK files/games, many of which that have been fixed/updated to run in newer versions of OpenBOR. But you have to download split files, rename the extensions, extract those to get a single 7zip file and then extract again to get the PAK file. It was a huge pain.
http://www.chronocrash.com/forum/index.php?topic=2360.0
Most of these are recommended for version 3979, which is used in the Android port. If we compile a newer version for the Pi, 3979 might be a good target. And using the Android port as a base (already compiles on similiar ARM chips, uses SDL, etc.) might make sense.
You could compile the latest and greatest, but fewer games might work oddly enough.
I'm going to go through the entire library of games I downloaded and see which ones work on the latest version, and which ones work on 3979. Then we might be able to put together a collection easily downloaded via torrent of OpenBOR games to play on an updated RetroPi build.