I can only state from being online for many years I can remember in the Late Ware / Main arena at times we had 350+ people online at one time on many nights. As time progressed and the game got stale those numbers started to drop.
Today the most I have seen online at one time in the Open Melee (Basically main arena) are just over 200 - and that is up from where it was I would say in the past few months where it was closer to 150 or so.
When I'm not traveling and home I am online mostly in the mid afternoon to very late evening my time (Pacific Standard Time / GMT -8) and the numbers vary from 30 or so (very late nights) to 200 or so during prime time.
The numbers will grow and you have to remember that the game is not being heavily advertised at all right now. It has been the existing base continuing to play the new version and also by word of mouth from those playing and HiTech's website. I think once we get to a fairly stable state of the game (which is pretty good at the moment but still things being fixed) the advertising will come and numbers will get better.
I think the thing that has made the game successful in previous years is the camaraderie, the simulation experience vs "gaming" experience, the community of players, and overall HiTech's dedication to constantly tweak and improve the game for all of our benefit.
Give it some time (as I've learned the hard way LOL) - it's getting better daily even though there are some frustrations.
Cheers,
Elec1