As matted said, from a SEO point of view it is very important you keep the old urls.
If you need to move a page from url1 to url2, you must use permanent redirects (htaccess is the simplest solution) to preserve old rankings.
HTACCESS EXAMPLE:
Code:
Redirect 301 /old_url.html http://www.website.tld/new_url.html
Another aspect is the CODE-TO-TEXT ratio: in my personal opinion, if you move from a page with 70% text and 30% code to a new page with the same content but with 50% code and 50% text, your page will lose some quality. Anyway it's just a personal opinion..