With one pump for both spa and pool, your builder is correct in that the low speed will not be sufficient for the spa but that is why you have two speeds. You run the spa on high speed for jet action and low speed for pool circulation. The high speed of a two speed 2 HP pump is about the same as a single speed 2 HP pump so there is not much difference at high speed for the spa.
An alternative configuration would be to use two separate pumps. A low HP (3/4) pump for pool and spa circulation and a high HP pump for just the jets. This should be more money than the 2 speed.
An increase of $500 seems a bit high to me for a 2 speed pump. The pumps themselves are less than $200 difference in price so he is padding it a bit.
As for the wireless system, when I bought mine, it was about the same price as the wired. The wireless remotes are quite nice since they don't tie you down to one location and can be used while working on the pool.
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