I haven't deployed with them yet, but have been seriously considering making the switch to Cloud66 (http://www.cloud66.com/).
It looks like the best of both worlds -- higher level than Dokku, but choices when it comes to the underlying infrastructure provider (Linode, DigitalOcean, AWS, or some combination). Small overhead charge for the management which seems very reasonable, otherwise you're just paying for the (virtual) metal from the IaaS guys.
We've been using Cloud66 for a couple of months now. You may find yourself tweaking the manifest files, though. It's not immutable architecture, but rather, they deploy over and over using Capistrano. So over time you'll build up some artifacts/cruft, especially if you're doing anything that generates a lot of log files. Not a problem, but you'll want to configure it to use instances with enough storage, which in a default config is often only 8GB.
I've been really happy with cloud66. Discovering new features everyday that saves me from having to build nginx/postgres/passenger from scratch. Try it out, I think you'll find it provides the balance you seek.
It looks like the best of both worlds -- higher level than Dokku, but choices when it comes to the underlying infrastructure provider (Linode, DigitalOcean, AWS, or some combination). Small overhead charge for the management which seems very reasonable, otherwise you're just paying for the (virtual) metal from the IaaS guys.