You don't 'need' them, but you might like them. Without them just leave a plastic retaining button out of the trunk liner on each side and you can pull it back to reach the adjusters. With these, you just drill a very small hole in the trunk liner and you gain access to the adjuster right there!
NC PRHT Note: The Power Retractable Hardtop version of the 06-15 cars has less space and clearance around the top of the rear shocks than soft top cars, and there isn't room to install these.
MIATA NA/NB 1990-2005 · Wilwood Dynapro 6 Piston
MIATA NA/NB 1990-2005