What's the best way to stay up to date with development?
I would recommend reading Github for Coders or the Ethereum blogs
https://github.com/ethereum
https://blog.ethereum.org/
To be technical heres a list
https://forum.ethereum.org/discussion/1495/chat-with-the-ethereum-community-on-skype-and-irc
Thanks! Is there a block explorer that shows the % of coins that the top N wallets like https://chainz.cryptoid.info/ltc/#!rich ? I know about https://etherscan.io/accounts but it doesn't show the % of coins that the top N wallets have.
Ethereum would gain more traction if it releases a GUI wallet. That way it would be a whole lot easier to send and receive Ether without any technical knowledge at all (for noobs). People would then become interested in it and adopt ETH for use in decentralized apps. A good idea would be to make a decentralized bank based on Ethereum. 
I agree, how can widespread adoption be expected without a GUI wallet? Most people only have experience with GUI programs and would not bother trying to use a command line wallet.