Not much, I'd imagine. The main reason for paying Poles in hand was that they couldn't work legally. Now they can, employers have far less reason to pay them that way.
none the less, the money sent to Poland creates a one way street. The avg. Brit earns money and pumps it right back into the system. if a lot of your country's money is going elsewhere, the economy is taking a hit.
I've been looking for an article I read a few months back, it had the estimated amount sent from the USA to Poland in 2010, I forget the amount. Anyway, the point being a lot of Poles in Poland have that apartment or that car or whatever because of money earned elsewhere. Millions of Poles have benefited from UK and USA money which I think pertains to this topic indirectly.
I'm happy to see Poland on the up and up but we cannot overlook the amount of "overseas earned" money being pumped in by the billions every year. Sure, they're going out there and earning it which is awesome to see, but it's worth mentioning because a lot of Polish people's recent success has been achieved through financial gains outside their borders. Stop money flow to Poland from the USA and the UK and you will see a very different Poland.
Even within my own wife's family, there are great success stories with US dollars to thank for it.