How many hits are you getting per day that isn't great performance? I'm running two WP blogs each on their own $5/mo plan and it's been working great with one notable exception: I would constantly run out of memory on my highest-trafficked site (20 uniques per day) with WP Super Cache turned on. When I uninstalled it, the speed went way up and the out of memory errors disappeared.
https://github.com/kevinohashi/WordPressVPS you can take a look at the loadtest_results folder to see. I tested a lot of different configurations and plugins. The default LAMP stack which DO provides starts to struggle at 10 users. While some configs were doing fine over 1000.
