I think the main point with someone like Bernard is that in order to snatch up a player like this you really have to have the courage of your convictions and act quickly.
Why is he valued at £12m (I don't believe this btw, I think he'll be more)? Because he has just had an incredible break out season and the world has paid attention.
Is £12m a risk? Undoubtedly, it's his break out season so nobody really has the skinny on him. He could be a one season wonder.
Is £12m worth risking? Undoubtedly, if he has the same level of success for a second term, his price tag will be minimum doubled and it won't be a Europa team that buys him.
If you want to get a player of this calibre but not pony up the real money for them, then you need to take a risk before anyone else. This can sometimes work out well (Modric), or it can bite you in the arse when you realise that you bought the wrong player of a wonderful strike partnership (Rebrov/Sheva).
It means plucking a player from a league you would consider inferior and with not very much experience. Look at ManU and Ronaldo. £12m for an 18 year old with a season of experience. Fergie's next attempt to steal a world class superstar ended up with £8m wasted on a street kid who had never kicked a ball in a top league. That's the risk/reward balance.
If this kid has half the potential people are bleating on about, then £12m is a calculated risk that is available for one transfer window only.