No one is going to be as enthusiastic about your car as you. And if you are laboring on someone else's car, it's easy to think of many other things you could be doing that day.
Some clubs have "Monster Garages" to tackle difficult/many hands projects and combine them with beverages and food for all. Small groups are much more manageable, along with once a month or so get togethers.
No one is going to want to pay in. It's hard to find incentive to help someone else pay for new parts for their car. But if the group has spare parts, swaps or gifts can work.
I've been in a few clubs. One met every summer Wednesday at the local drive-in. It was basically a brag session. Booooring.
Another was a local group led by a member here who was good at contacting all of us and getting us to commit to events. There were half a dozen or more of us who would show up with '69 Firebird 400 convertibles and do local shows and cruises. It was cool with the "birds of a feather" theme and we'd swap off parts too.
I am a member of H.A.L.F. but I've only been to two gatherings, and a member of POCI and haven't done more than read the magazine.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching