@Tarheelgurl: I get that you’re going for simple and elegant, but I think it might actually be too simple for your wedding, since you’re “requiring” formal attire.
Here are a few fixes I would do, if they were my invites:
Use different fonts. They look like Cambria and Calibri, both standard fonts for common documents. You don’t have to buy anything fancy, but just go down the list in your word processor and find something less common. In MS Word, I like Imprint MT Shadow (heavy text font), Castellar (all caps titling font), and Edwardian Script (script font for names).
I know this is just a mock-up, but can you do something about the borders? What color is your backing card? Black? Can you do a “border” of bright or dark blue cardstock, and lay your text paper on the blue cardstock?
Also, it looks like the blue ribbon is a way lighter shade than the blue text on your RSVP. Even if you’re using both shades of blue in your wedding decor, you should just stick to one shade in your invites. I suggest using a darker shade of blue ribbon.
Also, the ribbon bows remind me of curling ribbon for balloons. I’m not sure if it’s the thinness of the ribbon, or the double bow, or both. Do you like belly bands? That might look a little better, and you can use a dark blue vellum (if you can find some) or dark blue, thick ribbon and close that with a square of cardstock with your monogram on it.
I think the curved border is also a little awkward on the invite itself, maybe because it’s so close to the text. It would be nice if that motif were repeated on the RSVP also, since you have something similar on the Accommodations enclosure. You can play with the wording and spacing (line breaks) on the invite itself, too, to put some space between the text and the border. I know this is just a mockup of the text, but it’s redundant (“You are cordially invited…Please join us…”) and not formally worded (you shouldn’t use “cordially invited”).
I intended the above to be helpful, and not judgmental in the slightest. I like the other elements of your invitation a lot, and I think you’ve got a solid foundation for a great ensemble.