In all seriousness, and without the debate degenerating into a slanging match, it seems you're offering the online version of an "off the shelf" website. While that is absolutely fine for some, for others it is wholly lacking.
You cannot possibly extrapolate the satisfaction of your clients to the conclusion that web development is dying and not required, simply due to the fact that you personally would be unable to provide more bespoke services, either due to a lack of knowledge and ability, or even wanting to.
It's fine to build a business which provides a basic service but a basic service won't cater for those with higher aspirations for their business - and that's when real development kicks in. As well as real prices.
*Please* don't kid yourself otherwise. Aside from anything else you'll be denying yourself a decent living by devaluing your own service.
By the way, what happens to you when a developer decides to offer Wordpress installations for half of your price? What if that same developer CAN perform necessary updates and develop bespoke plugins, a service that you cannot? Bang goes your business. You're limiting yourself (and your clients) to what you know, on the assumption that there will always be something you can just slot into place. Risky.
Example: I can easily do your Wordpress installations. Can you build bespoke stuff to compete with me if I decide to do that? Hope so.