Is this about right? Has mining become such a commodity right now that you might hope to recoup only a few percentage profit over time on a capital investment?
Simply: yes
The only ones who are making real money with mining are the company's that produc mining equipment.
They first use it to mine themselves and when the return starts to slow down, they ship it to their customers. That's why all the pre-orders on the latest mining equipment exits.
+1 Yes
And there is another type of companies which make profit - like cex.io with their overpriced GHs and very very high fees (about 0.26$ Ghs/month).
Nowadays this is the only way to have a decent profit, more than just very few percentage.
SHA-256 mining lost its high profile potential a long time ago.
Also check this calculator and see it for yourself:
https://tradeblock.com/mining/