Whats the voltage your alernator is outputting? I wonder if components are being over-volted and burned up.
It sounds like the ignitor module in the distributor is crapping out. Its a mitsubishi made component, search ebay for "J208" you'll find it, thats the part number (may be listed for other mazda vehicles too). They used to come a lot cheaper than the few up there now. Generally this is the component that fails inside the distributor.
Whats the condition of the RFI suppressor on the top of the distributor? Its a little black box bolted down with a single wire attatched. Its supposed to filter RF interference and voltage spikes that can damage the ignitor.
Its just unusual for these to chronically fail like you describe, I'm trying to figure out what would repeatedly kill it.