Can I tell the wine from the cork? Previously I asked a question regarding nomacorc.  This has lead me to look more carefully at the corks that make their way into the boat.  Now assuming that we are prolific wine consumers (only for research purposes I assure you!), is there a way of knowing before opening/purchasing a bottle of wine if it is drinkable/good quality, or just plonk, from the cork?
Yes and No. Expensive wines are generally bottled in more expensive packaging because there is a greater profit margin and winemakers want to exude an air of exclusivity and expense. The unfortunately part is usually you can't see the cork because of the foil and the dark color of the bottle. 

But, if you could visually inspect the cork before you open the bottle, yes those that tend to use more expensive corks generally mean a higher quality wine. Screwcaps and plastic corks generally mean a lower quality wine, EXCEPT in Australia and New Zealand where there is a large push to use screwcaps for all levels of wine to reduce TCA taint. 

So, if you could look at the cork, these are the things you might look for. 

Cork Grading