Styling the date format with date_i18n

Just use date_i18n in multiple places with PHP date arguments just for what you need:

if ( $date = get_post_meta( $thepostid, '_sale_price_dates_to', true ) ) {
    $sale_price_dates_to =
        '<span class="m">' . date_i18n( 'M', $date ) . '</span> ' .
        '<span class="d">' . date_i18n( 'j', $date ) . '</span> ' .
        '<span class="y">' . date_i18n( 'Y', $date ) . '</span>';
} else {
    $sale_price_dates_to = '';
}