Again, thanks for all the replies. Lets see if I can sort through them and give some coherent responses. :) I think I am starting to understand how things works, but I may be wrong. ;)
I like the idea of a database backend as such, and I suppose it is correct that what I am using is a semi-dynamic setup. I am, in fact, already using MT's mySQL option, so a mySQL backend is just fine as well.
If I am understanding this correctly, I could migrate my site to .php rather than .html endings and then put the various php database calls (or whatever they're called) into as many of these .php files as I want to pull in WordPress content into, mixing it with the static content? And I could, for example, pull in all recent entries into one file, and in another I could pull in just a few recent entries from a specific category?
If my understanding is accurate, that sounds like it would work pretty well, since I could still work on the actual pages offline as I am used to. It'd just be a matter of finding a good way to redirect from .html to .php (but I believe it can be done in .htaccess) and learning at least something about how php works, in particular php includes to replace my SSI.
Can anyone recommend any good guides for starting off with php? I don't really want to learn the language, as such, just learn how to setup php pages and do some basic stuff. :)