The wordpress benefits are that you can easily add, delete or modify your content, without needing a lot of HTML or CSS training. You can also easily change the look and feel of your site by switching in new themes. Finally, you can easily update your WordPress install to the latest version, without having to mess with your content and theme.
You may have noticed the word “easily” several times in that last paragraph. Also, you’ll note that your content, theme and CMS (Content Management System) engine are separate and independent. So changing one does not affect the others.
In addition, there are thousands of plugins, most free, which allow you to add all manner of functionality to your site.
Finally, if you can’t find exactly what you’re looking for, you can create your own plugins or themes, or hire someone to do it for you.
Now, about your existing site. From what you’ve said, it sounds like you have over 50 pages of straight HTML. If you want to change anything on your page you have to go into an editor and change it manually. If you want to change aspects of the page template, you’ll have to change it in each of the 50+ pages. A CMS is much more efficient and convenient for that sort of work.
And now a caveat. You’re concerned about your Google juice, and rightly so. Moving your content to any CMS will undoubtedly affect your URL’s, in that they won’t be the same, and Google will think you’ve gone away. Luckily there’s a technique to maintain your pull with Google, and other search engines: it’s called HTTP return codes.
For each of your old pages you redirect the request to the new CMS page, and you give a return code of 301, which means “Moved permanently”. This indicates to the search engine that the content is still available, but at a new URL.
So, with all this in mind, My recommendation would be: it depends. Switching to WordPress is going to cost a certain amount of money. Only you can decide whether it’s worth it form a business perspective.
If your site is done, if it isn’t going to change much, then it probably doesn’t make sense to spend money on it. If, on the other hand, it is an evolving thing, if you’re constantly adding content, and you envisage needing changes to the template, and it’s making money for you, then it sounds like it may be a good idea to streamline those processes, and WordPress can do that for you.
I hope this helped.