I would think if you attend an event and "incur other expenses and inconveniences" to do so you would follow the guidelines unless you just don't care . The rules are easy and no one really checks your bike, but at least show up with the intent to look like you are following the guidelines. I have seen folks with bikes that are technically not within the rules but they are fine and they are there for the spirit of Eroica. Probably not a good idea to show up with a carbon bike with electronic shifting , but hey , it's up to you.