This is an interesting thought experiment and I like the specific framing of the question.

My initial thoughts are that this clearly would have been a good thing to try to work on, mainly due to the fact that the 2008 financial crisis cost trillions of dollars and arguably also led to lots of bad political developments in the western world (eg. setting the stage for Trumpism). If you buy the Tyler Cowen arguemnts that economic growth is very important for the long term then that bolsters this case. However a caveat would be that due to moral uncertainty it's hard to actually know the long term consequences of such a large event.

Here are some other ways to think about this:

Neglectedness

As Ramiro mentions below, very few people were alert to the potential risk before the crisis, so an additional person thinking and advocating for this would have increased the proportion of people thinking about this by a lot.

Tractability 

Even if you had predicted how the crisis would have unfolded and what caused it, could you have actually done anything about it? Would you just ring up the federal reserve and tell them to change their policy? Would anyone have listened to you as a random EA person? This is potentially the biggest problem in my view.

Other benefits - better economic modelling

I am a strong believer in alternative approaches to economic modelling which can take into account things like financial contagion (such as agent-based models), so a potential benefit of working on this type of thing before the crisis is that you might have developed and promoted these techniques further, and these tools could help with other economic problems. In my view this is still a valuable and neglected thing to work on.

Other benefits - reputation

An additional benefit of calling the alarm on the financial crisis before it happened is the reputational benefit. Even if no one listened to you at the time, you would be recognised as one of the few people who "foresaw the crisis", and therefore your opinions might be given more weight, for example the people from The Big Short who are always wheeled out on TV to provide opinions. You could say "hey, I predicted the financial crisis, so maybe you should also listen to me about this other <<insert EA cause area here>> stuff". 

Well, if your EA were particularly well placed to tackle this problem, then the answer is likely yes: they would probably realize its scalable and (partially neglected). Plus, if God is reliable, then the Holy Advice would likely dominate other matters - AGI and x-risks are uncertain futures, and reducing present suffering would be greatly affected by the financial crisis. In addition, maybe this is not quite the answer you're looking for, but I believe personal features (like fit and comparative advantages) would likely trump other considerations when it comes to choosing a cause area to work on (but not to donate to).

My (naive) understanding is that the risk of a recession today is not much lower than in 2007-08.

So the answer to whether EAs would be working on this back then rounds down to whether EAs are looking into macroeconomic risk today.

And the answer to that is mixed: there is actually a tag in the Forum for this very problem, which includes a reference to OpenPhil's program on macroeconomic policy stabilization. 

But there are no articles under that tag, and I haven't heard much discussion on the topic outside of OpenPhil.

What would it have taken to do something about this crisis in the first place? Back in 2008, central bankers were under the assumption that the theory of central banking was completely worked out. Academics were mostly talking about details (tweaking the tailor rule basically). 

The theory of central banking is already centuries old. What would it have taken for a random individual to overturn that establishment? Including the culture and all the institutional interests of banks etc? Are we sure that no one was trying to do exactly that, anyway?

It seems to me that it would have taken a major crisis to change anything, and that's exactly what happened. And now there are all kinds of regulations being implemented for posting collateral around swaps and stuff. It seems that regulators are fixing the issues as they come up (making the system antifragile), and I don't see how a marginal young naive EA would have the domain knowledge to make a meaningful difference here.

And that goes for most fields. Unless we basically invent the field (like AI Safety) or the strategy (like comparing charities), if the field is sufficiently saturated with smart and motivated people, I don't think EA's have enough domain knowledge to do anything. In most cases it takes decades of work to get anywhere.