Much is often made of Ed Miliband's alleged (and I use the word because I don't want to get into the area of the truth of the allegation or not) lack of policies, particularly on the economy. The blank sheet of paper that is so often referred to.
This is neither a surprising or bad tactic for him. It's very hard to sustain interest or a narrative over any length of time particularly in opposition because there's little to sustain it. It gets stale very quickly however good it is. It's an obvious point, but you can't spell news without NEW. Anything he launches now will fade and become played out well before the next election, not to mention if the situation changes it won't fit the situation as well and changing it will open him up to charges of flip-flopping.
Secondly he doesn't want to talk about Labour's economic policy because that comes dangerously close to talking about Labour's economic record and he really wants to stay away from that at all costs. When it's the economy he wants to do nothing but attack the Coalition and the current state of affairs, always on the attack. A foggy policy is one that's hard to hit.
He's got the basic theme which is less cuts and more stimulus and needs no more than that, particularly in the modern era of politics (the long decline of long speeches in favour of soundbites has leaned politics towards this notion). Specific policies just give the coalition to hit. There's a quote I've seen attributed to several people is
"The very first law in advertising is to avoid the concrete promise and cultivate the delightfully vague."
and what is politics but advertising. Ed will and should stay away from getting anywhere near specific about what he should do. At least until a general election is in the foreseeable future when he can start putting things together and be seen to be offering an alternative. An alternative that can be painted new as Ed's policy with no questions of altering past policy. If asked he can point to the vague statements and say "I've argued for more stimulus".
If you believe in the honourable contest of ideas, principled arguments, and alternatives being offered then you'll be disgusted at this tactic. If you're interested in politics you'll acknowledge the sense of it (and that Ed is very far from the first to tread this path).