No it is not a good indicator. The reason is simple: SatoshiDice represents maybe 30-60% of all transactions, but only ~5% of the volume of bitcoins. (Informal estimations based on block chain analysis, go here to get an idea:
http://blockchain.info/popular-addresses)
There is no simple and reliable indicator of Bitcoin activity. The simplest indicators can be very variable (eg. spamming the network with transacitions). Indirect indicators, like the number of merchants using Bitcoin are better. And looking at these indicators, it is very clear that Bitcoin activity is dramatically increasing. For example BitPay recently announced 10,000 merchants using their bitcoin payment processing platform (it took them more time to go from 0 to 1,000 merchants than from 1,000 to 10,000!).
This Techcrunch article was written by someone who did bad research and can't even draw correct conclusions from the graph :-/