I'm sure others will differ, but I tend to agree with the cheap tire/change often theory with the Sumitomos (or Kuhmos if you like them) for my STREET driving. I tend to drive less aggressively on the street - mostly cruising with the occassional punch out or hard corner.
But I'm starting to watch ebay for a second set of rims for track tires. The more I read and talk to others, this may be the best route for me. A set of street tires, given my use patterns, could go a long way and be very economical. Leaving more money on the table to put towards the track.
Those who drive more aggressively on the street will choose other options I'm sure, and rightfully so.