Are there Ethereum API wrappers? I'm looking into developing some Go software on Ethereum and I'm wondering - are there any API wrappers around for Ethereum (something like BTCSuite's BTCRPCClient is for Bitcoin)? I know there is a whole Go Ethereum implementation, but I'm looking for more lightweight way of interacting just with the JSON RPC server, rather than interacting with the whole network directly.
Not yet.

We've just revamped the server side RPC internals in develop and are still ironing out some quirks. I can imagine we would soon-ish start working towards the directions of providing some Go client APIs, but we're not there yet. If you just need a few specific ones, they are relatively easy to implement (here's a few we needed for a hackathon last week https://github.com/gophergala2016/etherapis/blob/master/etherapis/geth/api.go).