Is it still worth it or is the difficultly too high?
That depends on how much hash power that you can generate it from your mining rig. The price increase made more people tried to mine the coin like doge and that's actually making the difficulty increase.
Is mining low value coins still going on or are most resources now directed at the established GPU mined coins, albeit at much higher difficulty?
It looks like the majority of people were using asic and they have been leaving from the GPU mined coins. People don't wanna bet on the low value coins again except doge.
Any new coins on the horizon that may be worth a punt?
I'm not sure about this but less and less POW coin came to the market and the majority of POW coins were cryptonight coin. People have been moving to the POS.