I have just finished a bunch of work on this plugin to fix a number of bugs related to starting instances and respecting instance caps for spot instances. The plugin will now restart a stopped instance and always respect the instance caps. Other issues about the credentials working correctly in all regions should be fixed.
Before I make this release, I would like to have people test with the 1.30 Snapshot to see if there are any problems. Once this release is done, I will take some new features and move to require a more recent version of Jenkins.