I have done some work on this, e.g,. Simple estimation examples in Squiggle and Five slightly more hardcore Squiggle models. Overall I'd say that e.g., a Fermi estimates around how valuable going vegan is compared to donating to effective charities is doable (calculate number of animals eaten, multiply by elasticity of production, compare against an estimate of value of effective charity per dollar. For some of these: this post might be relevant). 

However, estimation is time-consuming and somewhat expensive, so my sense is that it's more meaningful for things larger than individual acts, e.g., how valuable would [random $1M intervention] be. Because for larger interventions, you are spending a smaller % of the time on the estimation.

That's my 2cts.