How about we don't add any classes, don't call it "spec" racing, and add one small item to an existing category:

SUPERSPORT (MW/HW/OP) -- Current rules apply but with this addition:

Any motorcycle 5 years or older than current race season is allowed the following modifications:

Unlimited chassis, suspension, intake, and ECU modifications
OEM wheels only (no mag/carbon/etc)
Unlimited motor modifications except the following:
NO OVERBORE ALLOWANCE
NO FORCED INDUCTION

DOT tires required for everyone

Contingency (manufacturer and other) rules apply as standard. (Meaning a 2006 R6 will not win Yamaha $, but can race the event)

A novice running a superbike (but not new model year superbike) is then eligible for a bunch of Saturday races without changing a thing. People who can't afford to update every other year to a new bike may be able to squeeze a few more years out of the bike through highly-illegal-for-supersport (but-still-done-by-some) modifications and keep the bike on the grid.

Those who are chasing $ on the latest equipment will continue to have the fastest motorcycle with the latest technology. But instead of just 4 bikes on the grid, there may be a few more.