The board room is used by the club. You don't rent a board room that isn't part of, or next to, your office.
If you want to run a corporate function, you hire somewhere more appropriate - even basketball events recently have been held outside this venue.
The number of people who think getting married at the Dome is a good idea would be less than about 5 in this state.
Depending on the actual agreement, concerts may not be permitted by the council. Unsure on this point but for a lot of the bidding process, restrictions were suggested as maintained. No church congregations, no computer fairs, no pet shows, no second-tier rock band concerts.
Assuming the restrictions were maintained, income streams would be 36ers game nights (16 per year), trainings, a social basketball competition, club home court (e.g., Woodville if they can afford it), maybe school basketball programs during the day when not being used by the 36ers, and not too much more than that.
(You are also making the assumption that two people bought two independent assets - I don't think that's a safe assumption and would explain the combined price.)
I don't necessarily think it was the steal that some are proclaiming it to be - if it were, there would've been bids higher than Groves' - realistically, it's a glorified shed, customised to one purpose (professional basketball games, not even professional and junior games!), on dodgy land, needing near-immediate and ongoing maintenance. The right people could make a good go of it (and Hemmerling and Groves look to be those right people), but it's not a bargain in my opinion (for what that's worth).