Amen to the intangibles, you said it right.
And you've convinced me about the project goal vs hourly return question. In your case, you also had a plan from the get go to keep certain aspects of labor to a minimum - the investment in mulch to handle most of weeds; drip irrigation too is a big time saver.
There are some assets that you develop which also have value in their own right not as something to sell but something to use. So if you own land for example, everything done to enrich the land and make it more fruitful is worthwhile, at the same time hard to put a dollar value on it. Fertilizers and soil amendments, I never regret the dollar spent and/or the time to get free stuff and apply it. Same goes for time spent saving or developing a seed resource.
Other type of assets depreciate as time goes by because they wear out. Thinking about fabric mulch, row cover etc. which are consumed in the process (over several years, but still). So it is kind of the opposite, you put money and/or time into it and then one day (always too soon) realize you have to replace it...
IMO at $25 an hour you don't even need intangibles to justify the time.