The big three do have clear benefits in terms of scale, reliability, and features, so I'd say it's worth it to look at "accessory" applications that run on top of them.

Looking at YCombinator's alumni, there are a few interesting ones - for example, CloudThread.io (no affiliation) tracks cost efficiency of teams and applications, providing "technical cloud cost unit metrics as a service."

My company, Usage.AI, automatically buys and sells Reserved Instances to cut EC2 costs by up to 57%.