Blimey! That cannot be the original chain, surely... But you sought advice. As follows:
1. Dirt and grime are nothing in terms of presence. Their only ill effect is that they wear away at things. Clean the chain and gears (using webheld counsel as advised).
2. Wear is a bad, naughty no-no for a bicycle chain. Measure the wear on it (using one of those metal tuning-fork things that isn't a tuning fork). If the wear is above what is helpful or rideable, bin the chain and replace it.
3. Although it just looks a little grubby and black when dirty, a cleaned chain is a wonderful thing. All my best times on leisure rides and my old commute have been done on a bike whose chain and sprockets I've just cleaned and lubed. It may be psychological, but I think it is also a matter of increased efficiency and all that hoo-ha.
I hope I have helped and I'm off to serve supper in the absolute conviction that I have.