I look at it like a stock broker. ROI: return on investment. What is the cost of LS swapping? $1500? engine, tranny, harness, PCM, tune, and what is the fuel economy differential. Perhaps 3 mpg? How long till it pays you back the MPG savings? 5 years? 7 years?
If you looked at it like a broker, you'd be thinking about your commission. Worthless middlemen.
Swapping out a good running engine should really only be done for smiles per gallon.