Pre-1999, the creation of a devolved Scottish Parliament seemed like a great idea. Scotland hadn't had a way to express its identity for nearly three centuries, and creating a forum for developing genuinely Scottish solutions seemed like a good way forward.
However, as times goes by, it's becoming increasingly clear that asymmetrical devolution (the construction we have in the UK, where there is no English Parliament and Westminster consequently has to act as the parliament for the UK and for England at the same time) is fundamentally flawed.
Proper federal systems (good examples are the US and Germany) work well and seem to be stable. No matter where you live, the local state handles specific issues (e.g., education) and other things are dealt with by the federal government. You don't feel any less American just because you live in Wisconsin instead of New York.
Centralised states (where there is only one parliament with law-making powers) can also work well (especially when the country isn't too big). Again all citizens are equal no matter where they live.
However, in the UK there are huge differences. If you're Scottish, your elected representatives have a say in both the education policies of Scotland and England. On the other hand, your Scottish fisheries minister cannot deal directly with the EU but has to use their English counterpart as an intermediary.
If you feel Scotland is different from the other nations of the UK, why wouldn't you want to opt for full independence and get the powers to control everything? And if you feel Scotland is just a region of the UK and not really any more different than Yorkshire, why do you need a Scottish Parliament making laws that gradually make Scotland more and more different from the rest of the UK?
When I look at Scottish Labour's hopelessly unambitious Devo Nano proposal (PDF), I really don't understand what it is they want to achieve. They probably thought the Scottish Parliament would be a great way to kill the SNP stone dead and keep Scottish Labour in power when the Tories ruled Westminster, but they now know they were wrong.
In their heart of hearts, I suspect Scottish Labour would like to roll back devolution and implement a proper One Nation vision for the UK. However, they know that would be political suicide in Scotland, so they opt for the smallest possible incremental change to devolution in the hope that the Scottish people will reject independence.
At the end of the day, devolution is probably inherently volatile and unstable. It will either lead to full independence sooner or later, or it will somehow get abolished again. Unless you believe Scotland is just another British region, you might as take the plunge in six months' time and vote Yes.