Wow, wow, wow!!!

I finally could make ShareWire to work in the Mac mini (turbo-charged connected to five hosts)!!!

I just replaced the following items of the Mac mini using the ones of the pendrive in which WireShare worked:

/Library/Java

/System/Library/Frameworks/JavaFrameEmbedding.framework
/System/Library/Frameworks/JavaScriptCore.framework
/System/Library/Frameworks/JavaVM.framework

/System/Library/Java

And then re-installed WireShare, which is NOT set as 32-bit mode by default (File - Get Info; it did not connect if 32-bit mode was selected, which is the installation default!!!). In any case, since Java 6 is not present, it always showed Java 1.7.0_67.

On the other hand, as previously indicated, WireShare - Preferences - Advanced
is set as default:
Gnutella port - Use Universal Plug 'n' Play (Recommended)

BitTorrent ports - Use Universal Plug 'n' Play (Recommended)

I think that replacing the
/Library/Java
was the one that did the trick, because previously I had replaced the other ones to no avail. Setting it NOT to 32-bit mode could have also fixed it.

So, problem solved. Here I leave it for future reference, in case it may help someone.

Many thanks to all and specially to Lord of the Rings for all the kind support.