The SNP likes to paint a rosy picture of an independent Scotland. They assume that with all that North Sea oil revenue, they could do just fine on their own. But the financial situation of an independent Scotland is not as they describe it.
For one thing, Scotland's main source of employment is government jobs. They don't produce much there, anymore. Even the Glasgow shipyards don't build ships like they used to. Way too many Scots are on the dole, too. As a constituent part of the UK, Scotland receives more in government expenditures than it provides in taxes. Even the lion's share in North Sea oil can't balance Scotland's books. An independent Scotland would be a poorer Scotland.
The SNP has also floated a plan that envisioned them using the British pound as their currency for a period after independence. This was immediately nixed by the UK government. Scotland could, of course, use the euro if they got back into the EU; however, there are problems with this, too. While the EU would be glad to spite the UK, it really doesn't want to encourage independence movements in its member states. There are too many smoldering regions like Catalonia who would love to follow the example of an independent Scotland. Countries like Spain are therefore not likely to want Scotland back.
Now, patriotism doesn't have to be rational. You can cry "Freedom!" Braveheart style and face all the difficulties ahead. But if your great desire is to be independent, why in the world would you want to leave the UK only to subsume yourself into the undemocratic quagmire which is the EU? This part of the SNP program, I think, gives you the key to understanding the current independence movement: it's a political pipe dream of bureaucrats whose greatest desire is to submit to other bureaucrats.
Scotland's a beautiful place with a kaleidoscope of unique cultures, but it only advanced out of terrible poverty and backwardness when it joined with England and got the run of the empire. In every imaginable way, Scotland has gained more from the Union than it gave up. And with the devolution of powers currently in play, it could revel in as much Scottishness as it could desire from within the UK. Leaving the UK is a romantic notion, but becoming a concubine in the EU harem is stupid.