I have a 3 way switch and a 3 way dimmer switch to operate two recessed fixtures, which worked fine for years. Now, both spots are dim. Doesn't matter if I use the switch with dimmer or 3 way switch without dimmer. The slide dimmer works to dim the lights, but the maximum brighteness using either switch is about 30%. Is the issue the dimmer, and it needs to be replaced, or possibly something else?
First replace both bulbs. If that doesn't fix it, open the three way switch and bypass the second switch and install a plain switch. If that doesn't fix it, it gets harder. You'll need to check resistance of house wiring at that point.
My guess is faulty dimmer with dust in the rheostat.