Symphony.

Is there a convenient way in Symphony to retain the field values of front-end form submissions? Are there any extensions, utilities, or useful methods of doing so?

I am not sure if you mean this, but i always use this xslt and post-xml data:

<input name="fields[name]" value="{/data/events/*/post-values/name}">
    <xsl:attribute name="class"><xsl:if test="/data/events/*[@result = 'error']/name/@type !=''">errorinput</xsl:if></xsl:attribute>
</input>

I also included the class attribute, so you can give your field a colour when an error occurs...
You can replace the "*" with your event name.

Hope this works for you as well!