Just like to jump in here...
Amiga.org is primarily a classic amiga site...the fact that it displays like sh*t on classic amigas is just plain WRONG. Percentages, technologies, everything else aside, this site should be visible on the most popular classic browser, and that is IBrowse.
There are a few problems with your statement. You can't throw "percentages" aside and then talk about "most popular" classic browser. I'd be willing to wager the vast majority of visitors to the site before moving to vBulletin were not using IBrowse.
In case you didn't read it, the site was updated to use a new forum engine because there was no other realistic alternative.
Here's a suggestion. I was thinking about doing this myself but I feel lacking in urgency since the only amiga browser I use here is OWB. So, why not learn PHP and write a proxy script that parses whatever page you requested, reformats it to remove all the CSS related guff, converting it (where necessary) to some tables based view and redirect all amiga.org referencing links to pass back through the proxy. Once it's working satisfactorily, ask the new owners nicely if they can make it run on a sub domain. The only tricky bits I can see is session management and the fact it would increase server load when it's used. However that shouldn't be a problem since a tiny percentage of users would actually use it.