For me, the most important thing to consider is how the world in general seems to be changing. Today, we are globalised to an extent people probably couldn't have dreamed of when we first joined the EU. Britain could doubtless survive without being part of the EU, but it wouldn't have the same political or economic clout.
We would still have a seat on the UN Security Council, G8, G20 and other international organisations.
We would increase our international influence by regaining our own World Trade Organisation seat.
If we remain in the EU our influence as a nation will decline as the EU seeks to fulfil the role on international bodies that we currently occupy.
I studied international politics at University and I really think most people don't fully understand how much our development over the past decades (as a centre of finance, technology, research) is entwined with our membership of the EU. It is convenient to most multi-national corporations to have their European base in an English-speaking country.
Our colonial past and Commonwealth contributed far more to this country's development than our relatively recent membership pf the EU. It suits banks and other financial institutions to base themselves in a stable country with a stable currency i.e. the UK. And that will continue after we have left the EU. Basing themselves in London not only gives them the benefit of the English language but shields them from the inevitable fallout from the Eurozone collapse.
All that aside, however, my "In" vote is based mainly on my own experiences. I was fortunate enough to spend part of my university course in another EU country, at no extra cost. I then spent time living and working in that country. I credit that experience with developing me into the person I am today and it would make me feel very sad that my children wouldn't have the same opportunity.
People from the Uk have been living, working and studying in Europe and European universities for centuries - long before the EU or the international Erasmus programme. and would continue to do so even after we've left the EU
As posted upthread, of course you need to speak French to get a job working as a waiter in Paris. Being part of the EU gives our children the ability to access European education systems easily so that they are able to learn the language.
Maybe in the spheres that you occupy but in the average UK household the ability to access the European education system is not high on the list of priorities. The ability to learn a foreign language is not high on the Government's lis of priorities since foreign languages were dropped from the national Curriculum.
Just a word about Turkey. The accession criteria for EU membership are extremely strict. Turkey has years, most likely decades to go before meeting some of them (most notably human rights), although it has made good progress in other areas. It first expressed interest in joining the EEC in the 1960s and hasn't succeeded yet. Britain has traditionally been one of the strongest supporters of Turkey joining the EU (perhaps based on its large economy and military resources?) while Germany has been the country least in favour. Interestingly, in a recent poll of Turkish citizens, only 43% were in favour of joining the EU
Turkey already has a customs union with the EU.
A recent ECJ ruling meant that the UK has to pay Turkish workers unemployment benefit.
Turkish has just been recognised as an official language by the EU.
The threat of flooding the EU with migrants looks likely to win Turkey not only £6billion of EU funding but also visa-free travel throughout the Schengen area. Cyprus's possible veto has been squared away.
Turkey is edging towards EU membership in all but name. Turkey only has to threaten to leave NATO and all those hoops through which it must jump to secure EU membership will quickly fall away. And Turkey knows that threats - like the migrant flood, do actually extract from the EU, what Turkey wants.
Perhaps Turkey may take decades to secure EU membership. But Albania, Macedonia, Montenegro, Bosnia and Serbia are in active accession talks with the EU. They may even leap-frog Turkey in gaining EU membership