Willing to put a bet down you could 3x traffic/conversion with design improvement.
I worked out one time Ive more than 300 million online sales/signups/downloads under my belt. I like to think that gives me some credibility. And I agree with OP that simple, basic and even ugly pages can be extremely effective.
Design is incredibly undervalued on HN, and I make contrarian claims to not only ruffle a few feathers, but because it’s a fundamental thesis of mine.
Note aesthetics are also a functional beauty to me, I enjoy both refactoring code and typesetting a landing page as part of the design process.
Fwiw, I think you're right. 3x is probably what the match of design and message results in, especially because a lot of what software does can't be described merely in words. It needs design to put the accent on the right things, or else will fail to communicate (most of the time).
Looks like we're reading different HNs.
Not sarcasm or passive agreesivesness. I'm genuinely interested in the data from someone in an agency.
The best client example is Groove (https://www.groovehq.com/). In 2014 they hired us to take the existing site (https://web.archive.org/web/20141223145657/https://www.groov...) and make it attractive to serious customers who can "trust" their company based on the site. Went from 1M ARR to 5M in 18 months.
A more concrete personal example is when we ranked "HTML Color Codes" with essentially zero feature improvements beyond nice UI/UX. Now ranked #1 in Google for several queries...making $5k/mo passively. More detailed write up on Indie Hackers (https://www.indiehackers.com/interview/growing-to-1-300-mo-b...).
I think your examples do not really prove the role of visual design conclusively because in the 18 month time-frame, the folks at Groove must have had several efforts running concurrently with the explicit goal of increasing revenue. The web site facelift you were engaged for happened to be one of the steps they took towards that goal.
For instance, they would have intensified sales, marketing, customer success, fixed bugs in the product etc in addition to the revamped website, so we can't really pin the significant jump in revenue from $1m to $5m on visual refresh alone.
Not trying to diminsh the work that you did, merely trying to put things in perspective because our tendencies as humans is to misattribute causation, which is bound to happen if all contributing factors to a thing's success are not properly considered.