The ShopBot people now have another brand (HSD) of high frequency
spindles available in 2.25 and 4 HP, both of which are available in
single phase 220.. which is kinda cool, as the electricians' quotes for
3 phase in my new shop are through the roof... at least for now.

The feed-back I'm getting, seems to be split into two camps:
a) buy what I think I am going to need
b) start off slow/small and buy what I need when the need arises.

...but you mentioned something very important...a spindle is much
quieter.

got three phase in my shop no problem at all there. I could run a 16hp
3ph motor.
but the problem with getting a router then upgrading to a spindle is
you would have to send the control box to them. that would not be
cheap.
mainly you get lack of noise and better accuracy. but for most people
I doubt the accuracy issue is much of one.