My ex- owners club has a national UK meet each year, with 80+ cars turning up

(Including some from aboard

)
It's a fantastic idea, but takes a
LOT of organising, and can end up costing a fair amount too...
The TT Owners Club did Silverstone this year, and Gaydon (motor museum) for the previous 2 years.
Once you get above about 10-15 owners you really need somewhere which can have a dedicated parking area (hence cost), and to make it worthwhile for people to drive a decent distance then means you need more than just 'meet up for a chat' (great though that is!

)
Not sure on the cost for Silverstone, but to hire basically the car paking at Gaydon was circa £1500 for the day.
That meant the public were still allowed in, but had to park in the overflow car park
Cost was subsidised by the owners club too...
But Audi did help out by bringing along their driving experience thing, and then letting us loose in 3.2 TTs round a bunch of cones
Great - no, fantastic! - day

BUT, the commitee basically finish the day knackered, and the next day start planning the event for next year

(partly cos we could never agree on anything

)