It seems unlikely that the construction material of the boiler would change the quality of the Espresso shot. What is more crucial, I understand, is the temperature stability of the entire machine, Brass has good temperature retention, yes, But if the thermostat is working correctly, it seems to offer no competitive advantage to stainless steel to have the boiler made out of brass or stainless
Of course, I could be wrong. but Id imagine its more important to look at the capacity of the boiler to make a proper judgement on whether the Basic is an upgrade of the Pure.
For my eyes, Theres little between the two in terms of ability, Itd be more like taking a side-step rather then a step-forward