PageRank.... you poor poor silly little man
Page Rank is a voting system, changing your site to SEF's now won't have much impact on it if you're internal links are updated (which I think you said you have)
And external sites should follow suit or new links would be created to new topics etc (I'm sure your software handles a direct link to topicid=14 and redirects to the new SEF link)
Where SEF helps is long tail keywords and organic indexing. For example:
"Diets" will yield 40597339582659736840958724936 website hits, but "diets for kids under the age of 12" would hit less websites.
So lets assume someone started a topic "diets for kids under the age of 12" and you have a SEF url in there. Google can pick it up much easier than topicid=67
Also remember, it takes months for Google to index all your site, and changing it now, expecting something to happen overnight won't mean it'll index it as fast. So changing and updating your sitemap is a good thing... Google downloads my sitemap at least every 12 hours, so it means the frequency of your sitemap changing wasn't that much and you had to do a manual update.
Back to Page Rank. The voting system... easy to get confused.
It's all to do with linking. Your home page links to 5 internal pages for example. And lets say your homepage has an incoming link from another site with a PR of 1.
That 1 then gets carried over to the home page, and split up into 5 (the math you can find on wikipedia, but this is what basically happens). So your incoming link "votes" part of its PR of 1 to your homepage, and your homepage then "votes" for each of your internal links with a bit of it's PR... and so on and so on and so on.
If those 5 internal pages link back to your homepage, your home page then gets votes from all those pages and then has a little more PR.
Ideally, if your incoming link does give you a PR of 1. And your internal linking is setup right, you could be seeing as much as a PR of 3 on your homepage.
This isn't factoring in any external links you may carry. Remember, the PR vote gets split up by how many links on your site, and if you give away a vote and the external site doesn't reciprocate, you lose that tiny bit of vote and your PR goes down.
Understand? So SEF doesn't have a big impact on anything if you have the external links coming in and handle the transistion from topicid=554 to SEF gracefully.
Google will just re-index everything anyway over time.
PR is an indication of how popular a site is, but isn't a true reflection of indexed searches or how well you're doing in terms of SEO. A lot of people worry more about that then SEO and gets confused... don't
