Valuing Companies Sanford

I normally buy shares based on the recommendation provided by ASB Securities and IRG.

If you were valuing a company what are the most important factors/ratios.

In the case of Sanfords although I don't have any hard facts I have the perception that fisheries worldwide are being depleted theoretically if a growing middleclass in China and India are going to drive dairy and meat prices higher this must also apply to fish. The NZ Quota system is a barrier to entry for competition and hopefully avoids the problem of overfishing. Long term I would have thought it is an industry with good prospects. The costs of fuel, labour etc are obviously high. Exchange rates will affect the company profits but that is something you just have to live with.
At $4.40 a share based on the Sept 2009 financial statements the P/E ratio is 10.55 (or inversely 9.4%)
Assuming intangible assets are mostly quota Net Assets per share are $5.85
Liabilities are 24% of assets (I don't really know how that compares to other companies)
Dividends haven't really moved over the years but provide a 5.2% yield (6.76% including Imp Cr)
The shares are largely held by a few parties but that does not bother me as I am not going to be buying large amounts. The tight shareholding may be keeping the sp up.
At a 5.2% dividend yield I am really banking on fish/shellfish prices increasing faster than fuel and labour costs.
How would you value shares in Sanford's and what would be the most important quantitative and qualitative factors.

The AUD/NZD cross rate has also been a massive boost for Sanfords as Aussie is one of their major buyers of fish
Also Quota prices have gone up massively over the years so Sanfords Quota holdings value is very high-Crayfish in the south for one like area 5 is currently getting sold at 500,000 per ton
not that many years ago it was worth no more than 200k