That's easy - market share and market dynamics.

I check for signs of plumbing leakage in the kitchen and baths and do a visual inspection for any noticeable damage.  

The refrigerant leak can be the biggest challenge - they must examine the tubing visually for signs of damage, leak-check the joints, coils and tubing using an electronic leak detector, and once they find the leak, the system must be depressurized (pumped into a refrigerant container), the leak repaired, then the system must be evacuated to make sure it holds a vacuum (verify no more leaks), then dessicated and recharged.

This is when a nice spreadsheet will help you visualize your cost/benefit analysis.

Is there a test to see if I'm better off replacing boards or is a visual inspection enough? 

For example my spreadsheet list on a home that rents for $1,000 the rent from the 1st - 5th is $1,000, from the 6th - 15th its $1,100, from the 16th - court date is $1,325 ($1,000 rent + $100 late fee +$125 court cost+ $100 reinstatement/admin fee).This gives them a visual picture of what they are going to owe.

If that ends up being your main MO for having your romantic partner sign a lease as your tenant--effectively permanently changing the power dynamic between the two of you--then I would double check with lenders first.  

And especially for the visual :) I had already painted the garage door a tan(ish) color to try to make it blend in more-- do you think I should go back and try white instead?

One of the other interesting dynamics in a price-crazy market like San Diego is the landlord-tenant interaction.  

I learned not to show units while occupied, mainly because applicants can't visualize their stuff in the apartment, if the current tenant's stuff is still there.