Shifted plates are always a concern in smaller elements. But there really isn't any advantage to rich black in small elements anyway since you won't notice the difference (except when there's a problem).
The bigger issue to be mindful of is overprint vs knockout. If you'll be using your black over photography at large sizes you have to remember that black is overprinted. A straight black is translucent, thus, will be effected by the photography beneath. Rich black not only gives you greater depth it also knocks out the colors you use in your black wherever it overlaps other colors (such as photography). This can give you more even color in headlines or graphic elements. The risk is, again, mis-registered plates: You could end up with halos around those elements.
Bottom line: If you trust your printer, rich black can create a nice effect on larger elements.