If you spend $70,000 fixing up your home, you should expect to increase the sales price by $35,000
I have great respect for your knowledge and wisdom, but disagree a little. I agree what you write is generally true but with exceptions.
Upgrading with fresh paint and carpeting is typically an expense that yields more return than cost. A common technique used by "flippers." And "staging" your home using a professional company is often very wise (typically for higher end properties.)
When I sold my residence, I received 5 broker price opinions (BPO) about value and what I should list if for. Not an appraisal, but all 5 brokers were long term, skilled, and knew the local market. I averaged all 5 and came up with a value. All of them commented that the kitchen and master bath were "tired" compared to what is expected in a luxury residential property.
I put about $45k into rehabbing those two rooms. I did some of the bath rehab as my father was a plumber so that saved $$$.
Not long after, I put the property on the market-- asking $150k over what the average value of the BPO's had been. Within a day or two, I had an offer for $20k below asking. Or, $130k above the BPO value which was prior to doing the remodeling.
My one experience doesn't mean this is a good technique. But as an experienced investor, and licensed RE broker in multiple states, why would I even do such a thing if my experience didn't show a return?
There are intangible factors. Spending money, targeted wisely, will increase the speed of how quickly your home sells. So ... what is the value of a home sale quickly, or one that sits on the market month after month without a buyer?
Again, I mostly agree with your view ... just saying there can be some targeted exceptions. Input and opinion from local brokers can often steer a seller toward those targeted results.