Seedlings can take the humidity, so 70-80% isn't over the top. thecuch makes a great point with using soda bottles for humidity domes- should provide a near instant humidity bump. 55% isn't parched by any means, but I try to keep my little girls at 70-75%, at least when I can control it to that extent.
How long would you keep the bottles on them? A week or so? or just until they are too big for the bottles?