There is a lot of mis-information about imports.
The fact is, some parts are the same, but a lot are not. For instance a 1989 UK MX5 bumper is about £250. The equivalent Eunos bumper is almost £600. Yes, the UK one would probably fit, but it is not OE and is not original fit.
I have to say, even as an "import friendly dealer group" (We supply the majority of genuine import parts over the whole south west), I would never personally buy an import Mazda.
If there is an equivalent model in the UK, such as the MX5 & Eunos Roadster example it isn't the end of the world, but with vehicles such as the Bongo van/ MPV/ camper people expect dealers to keep parts in stock, and don't understand when they are expensive and take months to arrive.
A local Autoglass had a Bongo come in with a smashed quarterlight. As this part had not previously been ordered in the UK or Europe we had to email Mazda UK to make the part available, they then had to contact Mazda Europe, who in turn have to contact Mazda Japan.
The glass in question was over £300 and took 13 weeks to arrive.
Another example with Bongo's is if you have a 1999> version the headlights are £830 each + VAT.
Incidentally from 2003 Mazda UK offer absolutely no warranty support for any Mazda vehicle sourced from outside the EU. The only exception is with safety related recalls, and even then the customer is liable for the cost of parts.