I’m sorry your clients aren’t impressed by your sketches. I haven’t found that to be true in my case. I have a few clients that have some of my early process sketches framed on their walls, sometimes from a decade ago… this is not a bad thing.
The master of the humblebrag 
Well, but here I think lies the difference between our points of view. You see a sketch as something that needs to “impress” someone. For me it is a useful tool I use everyday, but I don’t feel very emotional about it. It seems for you to be very important to be seen as very masterful at that particular skill, I personally don’t really care what people think about my sketches as long as they fulfill their purpose. I don’t think it is a designer’s job to impress with a purely technical skill.
I can go to artstation right now and hire someone to draw my product and it would blow everything out of the water anyone could do here on the forum, including yours, Michael. And there is no shame in that, because that person will be a professional, fulltime illustrator. This person would also probably charge me only a fraction of my current, hourly salary (and no, I don’t have an exceptionally high salary). Because drawing in itself is not a particularly valuable skill. I am not saying you should give the client shitty sketches that don’t “impress” him/her. I am simply suggesting that the client doesn’t give a shit if it was me who did the visuals or my intern. Because I am not selling myself as a colorful character, I am selling the solutions I came up with.
That is where I usually contract out work where as when I was younger I did a lot of that work myself. Now anything beyond a quick mockup to see if something might work or a print out of a tightly controlled curve to scale goes to one of my guys. To rationalize I suppose I have decide where to invest time…
Which is literally the EXACT reasoning I had for sourcing out hot design sketching. I hope you see the irony.