I'm running into an issue where I am generating floating letters. Everything works great except for the tiny little guys that do not get aliased properly and buzz from pixel to pixel. Blurring the source corrects this but makes the bigger ones too soft.
You can change the project's Render Quality to Best, which will perform higher-quality resampling on scaled objects, even individual particle cells. It's a project-wide quality switch, though, and you can't opt-out per object, so everything will be rendered that way, which may have a serious impact on performance. You may want to lock down the look of your particles, pre-render them in Best, then re-import to your Normal-mode project.