Having theĀ Event and Blog module able to Upload Multi imagess Like the Gallery Module all at once
Design and Skin Customization
The reason you're feeling some resistance from here to say "Great idea, we'll get that added!" is because the initial image is used as the definitive image for that event in lists, in media scan cards, in og:tags .....
If that single image for the event was changed to be a bunch of event images, then you need to define a specific image for the one to be used as the main image.
That makes the Event module different to how the Blog module works. The blog module has its main image for the blog thats used in the same way.
So the suggestion you got before to use the Form Designer to add a multiple upload image field for the extra images associated with the event and leave the current image for the events "Promotional Poster" image is my suggestion.
Then you can adjust the events item detail page and show all those extra images in whatever way you like.
It would be one extra form field added to your events creation page and you get exactly what you're after.
If you're unsure how to do it we can walk through it here if you like.