STL- Five-course dinner?
Let me suggest you continue with the 5 theme, as we did on our 9th anniversary. For our 9th, which was on Sept. 9 (i.e., 9/9), we flew up to Chi and had dinner at Steakhouse N9ne. I clued the restaurant in on the occasion and the reason for our choosing it, and they treated us like royalty. Thus, although I have not been to Five Restaurant in St. Louis, you may want to look for some feedback on it. Here's a link to the website: http://www.fivebistro.com/index_five5...
[Note: this is NOT Pujols 5.] It looks good on paper, and if it seems good to you, perhaps you can notify them of your occasion and also get rockstar treatment.
I think the place to get a tasting menu in St. Louis would be Niche. I'm not sure what An American Place is offering up these days. For a long time, Fiala's excellent restaurants The Crossing, in Clayton, and Liluma, in the Central West End, were offering four-course price-fixed meals with options for each course for $25, a spectacular bargain.