As a non-resident in England I don't particularly care for a particular result. If I lived in Scotland, I'd probably vote no, but who can say. The strongest argument seems to be political - especially if people are fed up of the three main parties that dominate the House of Commons. But it's unclear to me that Scotland's politics would be any better. One question would be if I felt that local people and politicians were closer to my views than nationally. For example, I think that's probably true for the city I live in, though not for the county. I have no idea what it would be if I lived in Scotland.
On all the other issues though, such as economy, I'd be worried about a yes.
An interesting consequence for the rest of the UK would be the 2015 General Election - the argument that even with a Yes vote, independence won't have been achieved by then. Which leads to the problem of whether you have Scottish voters and Scottish politicians in the 2015 election, and whether kicking them out afterwards means another General Election.
The final thing which annoys me about the process however is the requirement to be able to vote; if you are a Scot living in England you have no say. You'll be granted Scottish nationality if independency occurs, but because you've moved across the border you have no voice. While I appreciate that you could argue for some restrictions (the children born in England of parents both from Scotland not being allowed for example) but the fact that people who might have only moved for work a couple of years ago have no voice is just wrong imo.(I'm also not convinced about extending the vote to those aged 16 and 17; while I'm sure some will understand the issues comments I've heard about 'voting yes because they have a more positive message' speak volumes of the problem with engaging people of that age - hell, at 16 I wasn't in a good state of mind to vote but if I had at least I would have had better reasons than that.)
The only thing for certain, based on the polls, is that after Thursday there is going to be an almost 50/50 rift in Scotland between those who won and those who lost, regardless of the outcome, and that alone will cause a great deal of harm.
On the other hand, if I was someone living in Scotland who really didn't want independence, I'd be annoyed if the Yes vote was propped up by lots of people born in Scotland voting Yes for nationalistic reasons, but not living there, and not having to live with the consenquences (admittedly I don't know if Scots living elsewhere would be more likely to vote Yes or No, but I can see good reasons that they shouldn't be able to vote). Wikipedia gives another reason "In January 2012, Elaine Murray MSP of Labour led a debate arguing that the franchise should be extended to Scots living outside Scotland, including the approximately 800,000 living in the other parts of the UK. This was opposed by the Scottish government, which argued that it would greatly increase the complexity of the referendum and stated that there was evidence from the United Nations Human Rights Committee that other nations "might question the legitimacy of a referendum if the franchise is not territorial"."
Your example of a poor argument from 16 year olds apply to people of any age - on any political issue, I've seen arguments along those kinds of lines, for all ages.
This isn't just an issue for the next 4-5 years, it's an issue that will affect the rest of their lives, so I can see an argument for including them. Another reason though is that a voting age of 16 is SNP policy for all elections, so it seems more consistent to allow them a say before independence might happen.