No unclickable links

You're suggesting what is called "empty links." While not unheard of, this is actually considered poor practice. Having clickable main menu items, even when they have drop-downs, is not only considered standard practice, but BEST practice. Not only for accessibility, but for SEO also.

Whether a menu item goes anywhere or is there for filler, the way WordPress menus work is it will still be a link. And having empty links in your main menu (or anywhere on the site) more often than not causes confusion. Additionally, redundancy occurs (for example, you have an "About" page, so you'd also need that "About" page link in the drop-down menu causing a redundancy). And you'll get dinged by search engine spyders for having that empty link, hurting your SEO.

It's also bad future proofing. For example, if you end up adding a sub-menu item to another main menu item ("Events" or "News" for example), you're then hit with a conundrum - keep the original main menu item a link or turn it into a filler link, also which will confuse users who were previously able to click on that link (or causing additional confusion as to why one main menu item with a drop-down is filler and why one isn't). 

We highly encourage you to keep main menu items as actual links.