The ER series of collets will keep the tool concentric with the
spindle. If your already using a drawbar/collet style tool holder
(couldnt find the info on Taigs site), then I dont think youll see
much of an improvement considering the runout of the non ER spindle
is 0.0004" and the ER spindle is 0.0003". In addition, with small
machines, running the RPM’s up that high could introduce more
vibration to the machine since the drive motor sits off the side of
the head like that.
If your experiencing inaccuracies in your work, I would first check
the runout on the spindle with a tenths dial indicator. If that is
good, check the backlash and also see if there is any play in the
gibs/ways, they might need tightening/adjustment if the machine has
been used a bunch.
The only advantage of ER series of collets, like you mentioned, is
the ability to hold a variety of different diameter of tools, and
keeping things concentric.