I think your mistake is limiting it to winter. It could be a road cycling park with a closed set of loops open to the air for much of the year, with wide roads that could accomodate large packs of cyclists. Amateur, even professional cyclist could come to cycling camps to learn to ride in pacelines and pelotons or just to train or ride for fun, away from car traffic. Once in a while it could host actual road races,.criteriums, etc.

Then for a few months a year, when it got too cold, some or all of it could be covered fairly economically (I think) by a row of linked inflatable domes, arranged in a circle or figure eight, with passages between them so they are all at the same pressure and you can ride continuously through them. Expecting smaller crowds, you could install a median barrier along the track to make it two way, thus doubling your distance, but restricting the number of riders who could ride abreast. It wouldn't matter too much if it only broke even in the winter, because it might make good money in summer.