Currently we have 32k season ticket holders. For most clubs this is not indicative of a business that would struggle to sell 55k out most weeks.
The reality is every week for the past knows how many seasons we have sold every ticket that is not an obstructed view out. For a lot of games they are sold out too. This season every game will be sold out, minus empty seats within the away end and segregation.
Put simply 40k (or 39k) is much too small. This has also been done against a backdrop of 2 11th place finishes, our worst home record in our history and being trophyless for 21 years.
After the FA cup win (1995) our average attendances shot up by 50% from the 20's to the 30's. Some of this has to be accounted for with the growing popularity of the league and wider trends but there was undoubtedly a big jump on the back if winning something. I would say if we were to win a major trophy we would probably see a 30-35% increase in crowds (which is my estimate for the difference it made in 95).
Currently it is difficult to estimate what our natural average would be as we sell out every week. If we had an unlimited stadium I suspect our average at Goodison with no obstructed views would probably be around 45k. With a 30% increase on that that may come from a bit of success are excitement of a new beginning (akin to the mid 90's) you have another 15k. That gives us 60k. Even if I were to take the more cautious estimate of 39k and add 33% onto this we end up with 52k.
There is also added potential with it being a top class stadium in a world famous area like the Centre of Liverpool on world famous docks. Over a longer period we would see increased external interest. You also have to factor in the premier league looks set to continue to grow in popularity with 3 years worth of bumper TV deals and widening access for all teams. I'm not sure a % figure can be easily put onto that but it would be in addition to the 52-60k figures I have suggested.
I think these figures are a more realistic starting base than looking at what our attendances were in either the 80's or the 60's. The 60's when we averaged more than anyone was a half a century ago. It was a different world and a completely different game. Tickets were the equivalent of about a tenner.
Likewise the 80's is a poor example. Yes we may have only averaged mid 30's even when successful, but Liverpool only averaged low 40's and United were mid 40's. Clubs like Arsenal, Spurs, Aston Villa were all getting gates in the 20/30's. The reality is football was deeply unpopular (relative to today) and more of a niche sport.
If we can build a successful team that wins a trophy or can get into the top 4 I have little doubt that in a ground with no obstructed views we would be averaging towards 60k. If we remain where we are as a football club I would imagine our average would be close to the mid 40's and with a new location would push towards 50k. This stands a good chance of growing year on year.
The club have done some fantastic work in enticing young fans. Over the space of 10-15 years we have seen kids season tickets at under £100 and we have a remarkably high number of young fans as season ticket holders (I thought it was now 10k? under 18?). If simplistically we say that there are 1000 new young season ticket holders (to replace a 1k who graduate) over a 10 year period it means you add 10k to your average. I would estimate 50% remain season ticket holders after graduation, but it's still a 5k increase every year. It slowly builds a loyal basis which we are seeing the benefits of.
Anyway a long post. I wouldn't be fixated on capacity. I'd rather have a fantastic ground in a great location holding 50k with great corporate facilities than a box in Kirkby holding 65k. That being said I wouldn't be worried about selling out a 60k stadium. If we were successful we would sell even bigger stadia out than that, but that's the big if.