In order to be 100% sure that we haven't forgotten anything with all the new install.xml I would propose to:
1) Make one clean install of Moodle 1.7
2) Make one clean install of Moodle, 1.6 and upgrade it up to 1.7
3) Compare (with phpMyAdmin) that every table/field is exactly equal and that we haven't forgotten anything, annotating all the differences found.
It can be done in some hours and will allow us to start thinking about to drop all the old .sql files definitively (plus being 100% confident with the new tables).
Ideally, this should be performed both under MySQL and PostgreSQL, although checking it under the first could be enough... assuming that PG is 100% up-to-date with MySQL. Your decision.
Marked as blocker. Not sure if this is too much, but I think it's a must.