exactly
West Ham went from 35,000 at Upton Park to 65,000 gates and filled it by selling seats cheaply
obviously their plan was then to increase the prices in later years on once people got used to going - which seems to have worked out despite their supporters constant complaints about hating the stadium - so the plan to build the supporter base has worked - but happily not much else at their club!
If Palace went from 26,000 to 41,000 we could sell those tickets in the premier league with aggressive pricing - but moot point as it'll be years before we get to 34,000 and I doubt we'd need many special offers to sell the extra 8,000 in the PL