Hey All,
I'm wondering where this questions came from, because if the official answer really is E (as you seem to say), I can't agree. It draws the wrong connection.
Conclusion: British people have more money to spend on vacations now than they did 30 years ago.
Premises: 30 years ago, small percentage of British vk'd abroad. Way more now. VK'ing abroad is expensive.
Assumption: It has anything to do with money.
(A) If foreign travel had been less expensive 30 years ago, British people would still not have had enough money to take vacation abroad.
Problem: We don't need this to make the argument. In fact, it weakens our argument. We want people to travel if they have enough money to do so.
(B) If travel to Britain were less expensive, more people of other countries would travel to Britain for their vacations.
Problem: We don't care about people of other countries.
(C) If the percentage of British people vacationing abroad was lower 30 years ago, then the British people of 30 years ago must have spent more money on domestic vacations.
Problem: Domestic vacations are not part of this argument either.
(D) If more of the British people 30 years ago had had enough money to vacation abroad, more would have done so.
Answer: Let's try the NOT test (if we take the opposite of the correct assumption, the argument should fall apart) to prove this one. "If more of the British people 30 years ago had had enough money to vacation abroad, more would NOT have done so." Now we have a problem. The passage wants to link the taking of vacations with having enough money to do so, but this now says that when people have enough money to travel, they don't necessarily do so. That destroys the point.
(E) If British people are now wealthier than they were 30 years ago, then they must have more money to spend on vacations now than they did 30 years ago.
Problem: This is linking money in general to vacation money, but we're not concerned with money in general. If we take the opposite of this ("If British people are now wealthier than they were 30 years ago, they do not necessarily spend more on vacations") [paraphrase], the argument is still fine.
Not sure where this question came from, but if the answer IS E, I'm not seeing it.
Hope that helps!