Very good point, that would definitely help the new users understand the workings of Monero.
Yeah, and not just new users. I'm still trying to get my head around how Monero works and I'm looking forward to seeing just what a blockchain explorer can, and cannot, do. What is the most that can be gleamed about a transaction when is 0 vs greater than 0? Can you track ? etc.
The original post announcing Monero lists the following as some of its key features:
Quote
Untraceable payments
Unlinkable transactions
[...]
Blockchain analysis resistance
[...]
Unlinkable transactions
[...]
Blockchain analysis resistance
[...]
Your tool can help a wider population understand how elegantly this is true.
I'm also not very familiar with the inner workings of Monero. I'm able to extract from the blockchain some more attributes than the ones currently displayed on the website, such as the payment_id present on some transactions, but I don't know the meaning of most of them.
One of my next steps in my todo list is reading the cryptonote paper, so I can understand the protocol better and display the data in a more meaningful way or derive new useful data, to the extend possible.
Total coins in circulation might be a useful stat. People are always throwing around estimates, but you can calculate the exact sum.
Done! I've added a bunch of charts, including the one you requested: http://monerochain.info/charts
Top wallets would be great if it is possible 
Great effort here. Thanks.
Great effort here. Thanks.Unfortunately (or not), I don't think this is possible. As Kyune pointed out, one of the main points that make Monero different than most of other alt coins are its anonymity features based on ring signatures, which make it unfeasible to extract meaningful info regarding individual wallets.