This is a tricky one - so many Groups I think don't realise what a good thing they have by having a Scout Hall. Certainly my group is very lucky to have a hall, which cost very little to build at the time (about 50 years ago - it has been rebuilt since!) but the land it now sits on is worth twenty or more times that.
It is difficult to build a hall from scratch now, with so many additional costs involved and legislation to jump through.
But if we didn't have a hall, I would still recommend we built one. My reasons would be similar to yours:
1. It does unite the sections into one group. You have a shared common purpose - keep the place tidy, upkept, nice etc as it is only you who will use it
2. It forms a group identity which isn't the same in church halls/schools etc - kids know they are going to scouts when they go to a scout hall, and they feel an increased loyalty to that troop because of it
3. Security - not physical security but future security - a group near me folded because the church they were meeting in one day turned round and terminated the agreement they had with them. They were turfed out, and after trying to share with us for a few months, gave in. Twenty kids were out of a Scout Group. Having your own hall ensures that you have somewhere to meet for the future.
4. Fundraising - we rent our hall out Mondays, Wednesdays and Fridays to a play group which meets from 8am to 5pm in the hall. We give them the main hall and kitchen for the day, and one small storage cupboard, in return for a substantial donation. They can easily afford it as childcare is a booming business these days.
5. Additional activities - you can quite easily organise an activity for a Saturday at short notice when it is only your own bookings to think about - not so easy in a church hall. Also things like a jumble sale or similar - you can block off a week where you pile loads of junk in your hall and then sell it all at the weekend - again, not possible anywhere else.
6. Again, the future - it might be okay to store your gear in a leader's garage etc, but is that a good plan for the future? I know we need to think about that as we still store all our camping equipment in a former leader's (huge) garage, but how long until he passes away or we lose the connection?
Wow! That was longer than I intended.
Ultimately, it is a HUGE decision to make, not just the initial choice to go ahead and fundraise the capital, or to actually progress a building plan etc, but the long term decision to upkeep the building, insure it, heat it, pay the bills, clean it, and upgrade it in due course.
But in three words, my advice would be GO FOR IT....
Hope this helps!