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's the status of alternative full node implementations?"