I think you have a good approach to this, and so, all things being the same, a refresh of the site should not hurt.
You mention that "content, url structure, internal linking structure" will all remain the same - if this is true and you keep everything in this bracket 'as-is' then you should be fine.
The most common reason rankings are lost when implementing a new site is re-directs, or the lack a redirect strategy to be more clear.
As your site structure / url structure is going to remain in-tack, then you wont really need to consider mass redirects.
However, here is what I would do just in case:
Before Launch:
Create a report of top linked to pages using Open Site Explore
Create a report of top content from the last few months from Google Analytics
Map all the URLs from the current site, use screaming from or something
After Launch:
Submit XML sitemap to webmaster tool
Review and improve on-page content
Monitor traffic in Google analytics, view top content for the period after launch and compare to the report you created prior to launch
Monitor and fix crawl errors in webmaster tools if any
Attract new links
Submit new XML sitemap (two weeks post launch)
Keep developing great content