I'd like to suggest that the HQ is expanded to include a corporate hospitality. Perhaps the staff morale facility can be replaced with it (i don't really see the use of staff morale buffs anyway).
However, a facility which, when levelled up, will increase the pool, or funding given by sponsors would be useful i think. For a start it would add a strategy element to the decision on HQ upgrades - do you upgrade for more car parts per race, or do you invest so that you can get higher-paying sponsors next time?
This would be best implemented hand-in-hand with some way of seeing beforehand what the sponsor expectations would be. Too many times i have picked a sponsor only to find out they expect me to win every race in a league where i am the underdog!
In terms of balancing i'm pretty sure that having a level 8 corporate facility would be great, and loads of surplus cash would be piling in, but the downside of that could be that the better sponsors will have higher targets. This would make it clear that upgrading this facility is strategic.
