I think you can change focus for RSS feed add-ons. For example "RSS feed for Wordpress", "RSS feed for Xenforo" type add-ons will be better. You can add special features (phrase limit, photo width etc.) in add-on settings with this way.
You can use a RSS feed creator like Feedburner to create summary feeds of your Wordpress site (content will be truncated with ... at the end). Other options exist as well. I'll look into the CSS fix for this, but agree with Andy truncating the actual HTML content is non-trivial. You can't just chop it off, since all the HTML tags will be left unclosed and your page will blow up.