sanvila

Of course it is not a good idea, but that’s precisely why I call this a workaround and not a solution. A workaround is usually better than nothing.

Found a workaround:

https://www.ads-software.com/support/topic/password-protected-pages-are-not-working-503-service-temporarily-unavailable?replies=4#post-5127844

(only for the password protected pages problem on 1&1)

Same here. Using 1&1 and password protected pages do not work.

But I have just found a workaround:

ssh yourhost
cd your/wordpress/directory
ln -s wp-login.php password-wp-login.php
nano wp-includes/post-template.php

and then change

wp-login.php?action=postpass

to

password-wp-login.php?action=postpass

Hope it helps.

See function function upgrade_all() in file
wp-admin/includes/upgrade.php for WordPress 3.1.2. It performs all the database updates in order to upgrade from any previous WordPress release, like this:

if ( $wp_current_db_version < 2541 ) {
upgrade_100();
upgrade_101();
upgrade_110();
upgrade_130();
}
if ( $wp_current_db_version < 3308 )
upgrade_160();

if ( $wp_current_db_version < 4772 )
upgrade_210();

if ( $wp_current_db_version < 4351 )
upgrade_old_slugs();
[…]

So, yes, it seems what you want to do is supported in theory, as far as you copy the Media Library to the new WP install.

In either case, I would try on a test machine first.