Conceptually I think it's great for pipelines or use-cases like this, VMs are generally a terrible level of abstraction for a lot of problems, and the Lambda style promotes better architecture because of this.
The connectivity between Kinesis/SNS and friends is great. I'd agree that Lambda is not currently a good fit for "regular" apps, APIs should be fine now that the proxy stuff is in there, though there's slight latency.
No need to worry about gracefully stopping or restarting daemons, just push new code and the old stuff goes away, it really is a great abstraction that way. Basically replace anything you'd use a Go channel for, with more Lambda or SNS->Lambda if you need retries and backoff, it'll spare you a lot of code.
I find the workflow great as well, the slowest part for me is compiling the Go binaries, the rest is virtually instant. Especially now with all this needlessly complex Docker stuff it's refreshing to use something simple.
Cost is prohibitive for sustained use, so make sure you price things out properly, it sounds very cheap until you look at say a constant 100 requests/s behind API Gateway. It's easily 300-400% what you'd pay on EC2.
Cold-start is really a non-issue in most cases, it seems to take very little to keep a function warmed, so unless you get zero traffic (which would be dirt cheap on a t2.micro anyway) you'll be fine.