I think you are being conservative. Back in 2006/2007 it often traded above 90% of book value and was above 100% for several quarters I recall. The ROE back then was around 8% or 9%. During prior market cycles, it had also traded up into this range.
When I look around the industry, pretty much all life insurers are trading at substantial discounts to their mid-2000's valuations. Most charts are similar to NWLI's as well. As the overall interest rate and financial market environment improves, I really believe investors will pay higher multiples across the industry, so getting back above a p/b of 0.9 seems pretty realistic.
I think, being optimistic, would think we could get to book value this cycle. All lifeco's are trading at a discount because of interest rate concerns and general financial stock avoidance. Once the financial markets normalize, this industry discount should fade and, NWLI, with it strong track record, excellent balance sheet, and now (hopefully) better capital markets management, should get a much better valuation.
You see the large Japanese lifeco's coming in with their excess capital and buying up many of the smaller life insurers. By the time the market for life insurers gets better, there will be many fewer choices than there were say 10 years ago.