EntityFieldQuery - ordering by multiplication of two fields
If you don't have to pull in a whole bunch of linked entity stuff, just run a regular db_query() joining your "importance" field table to your node table.

$query = "SELECT nid, (created * field_importance_value) AS weight
FROM node n 
JOIN field_data_field_importance f ON f.entity_id = n.nid
WHERE type = 'news'
AND status = 1
ORDER BY weight DESC";
$result = db_query($query);
// Add foreach loop here...


I'm just guessing the importance table name and field name from your OP.