Christ, I come on line this morning all bleary eyed and it's like walking into a pub punch-up

Shall we rewind to the beginning and start again?
Hello Tom, and welcome. There's plenty of evidence that ZXRs are going to be a future classic. They are one of the more expensive 400s and becoming sought after. Now is a good time to buy as prices are about as low as they are going to be and there are plenty to choose from. As more get trashed / abused the good ones will be harder to find. It won't be too long before bits start getting hard to source and the first to get scarce will be bodywork, clocks, exhausts etc. The bikes that will command the best prices if they become classic are those which are standard, so think very carefully about doing something irreparable to it (respraying bodywork in a non-standard scheme, hacking undertrays to bits etc.). Modding by swapping parts is fine, especially if you keep the OEM bits you remove as you can offer them with any subsequent sale to a buyer who wants standard.
Don't forget too that modding a 1990s look to bring it up to date (LEDs, shorty levers etc) will look out of date in another 10 years. So then what you you got? A bike that looks old but not even original old. Remember coloured screens...........? Good mods never date.