Do you like the style of fireplace or is it the color you don't like?

The fireplace opening needs some enhancement. I am the owner of 2 lava rock fireplaces and I hate them both! They catch a lot of dust but I really just hate the look. When I remodel it will be torn out and replaced with the more contemporary low horizontal flame surrounded by tile/granite.
Your house is open allowing for a great focal point yet to be designed!

I dislike the rock and I dislike the test patch even more. I would have it torn out.

You could have concrete wall panels cast to fit the fireplace floor to ceiling. it would give you a modern clean look and you wouldn't have to demo the current fireplace. The panels would go right over the stone. The panels could be cast in any color you could image and they could be polished to any sheen.

one word... DEMO!
I dont think anyone even back in 1969 liked these lava stone fireplaces. Nitemare to clean and painted looks even worse.Ive demo'd many and redone a surround for the fireplace.. added built ins.. etc.

Paint it white and mount a waterfall on it

It is possible to perhaps overlay it or partially overlay it - and add some layering detail to the area. If the stone is difficult to clean you may want to consider this because of the future maintenance involved. Keeping in mind what the fire code is for whatever material you use on the surround. You can also add some asymmetrical details which would give the area a more "elongated, linear" feel such as a linear bench type mantle underneath the firebox area but not have it run the whole length of the fireplace and/or staggering shelves off to one side of the fireplace. An inexpensive fix would be to paint the rocks in a completely unexpected color like a Wasabi Green but making sure that it is a color you can obtain in a high heat area.

I'm the owner of the same ugly rock. Now that I can see what it would look like painted I'm definitely knocking it out! Although I love the waterfall idea...

I have the same lava rock. It is hideous and people who say otherwise, just haven't seen it close up. What did you end up doing?

Not to mention that the scale is way off between the massive Flintstones inspired rock wall and the teensy afterthought of a fireplace. Demo the lot!

Ugh...The fireplace was really ugly! Its homeliness motivated us to take action. Appearance ended up being the least of our concerns, however, as you will learn as I share this story.

First, we attempted to smooth the high areas of the basalt rock so we could reface it with culture stone. That did not work out so well...a corner began to cave in. We discovered there was inadequate support behind the rock. We also discovered that the fireplace itself was not sitting directly on top of the fireplace downstairs...It was off to the side and sitting on the floor!

Redoing the entire chimney/fireplace was not what we had planned; however, it was necessary. Serious problems that weren't obvious at the beginning may have proved disastrous. For example, the chimney needed to be higher to meet code after new trusses were installed. The added weight probably would have caved in the floor. We also discovered later during demolition the flues were cracked, and there was evidence of chimney fires.

We demolished it and constructed a new
fireplace. I have pictures of the entire process, but here is a picture of what it looks like tonight...

Wow! That was quite the journey, I personally would love to see the process pictures as a veteran of many renovation "surprises" ! I think the TV shows make it look WAY too easy and it helps to see the realities involved. And I must say your final result is spectacular!

Fantastic! So much better IMHO. Thank you for sharing.