Does running an alternative full node implementation benefit the Bitcoin network? I've seen discussions suggesting that
a monoculture of full nodes
is a risk to the security of Bitcoin.

The accepted answer
to the question
"What benefit does a non-mining client provide to the network?"
gives an explanation with regard to full nodes in general.
I'm interested in alternative full node implementations in particular,
ignoring any wallet or wallet API capabilities.

Let's assume that
one or more alternative full node implementations
can run the protocol reliably and accurately.
What are the short-term and long-term benefits of running such nodes
compared to running the Satoshi client?

Edit: See also "What&#39;s the status of alternative full node implementations?"
If all bitcoin nodes run the Satoshi client then they are all affected by the same bugs. So other implementations of the protocol will certainly help in this regard. Imagine that the Satoshi client was affected by a bug that when a certain date is reached or a certain event occurs, it somehow causes the blockchain data to be corrupted or even deleted. The bitcoin network could even grind to a halt. This is quite an extreme case but it's just to give you the idea.
If alternative implementations were widely used, only part of the network would go down.
All implementations only have to agree on the bitcoin protocol, so they would still be vulnerable to bugs in the bitcoin protocol itself, but there are hardly any bugs in it, and even those could be fixed by changing or extending the protocol.
There are some known bugs in the bitcoin protocol, like for example its inability to handle dates bigger than 2106, but it's not considered a serious problem and by the time that date approaches a solution will probably be found.