I think, that places like osowa, rumia, banino, pruszcz are really attactive. But I also think, that prices are going up, and they will be, but not so long, becouse thay are already high as for Poland. Last year flat' prices had grown about 80-100% which is depandeble of city and region. Houses prices didn't grow so fast - actually they didn't riase at all.
You're right about convertion - it would be a good way, but flat's sqm rates are higher than houses sqm rates. sqm rates for apparments will not go much higher because of polish socity debt abilities. Foraigners are not purchasing so much to calculate them as a strong segment of the market. They are important segment, but not necesserily strong

As I observe the market I think house's sqm rates are about 50-70% lower than for flats and appartments. That's why I wrote that market is going to regulate it itself, and house's prices are going to grow about 60%.
Places like you wrote are not full of appartments, so thee is going to be a developer's boom, and many building will be build. But for now, most of these areas are coverd with small houses, low building and so... most of the appartment building are old, and new are just developing, or going to be. And like that is almost everywhere in Poland. That's another point for me thinking that appartments prices will not go up this year, and if, it won't be much.
I'd realy convert my own house into two three flats, because flats market is much more fluent - as all over the world is

because it's cheaper. But to be honest I'm not sure if I wont loose on such a transaction - not saying that it's almost impossible to do. The hose is to comfortable. It's well advertised, but still I can't find buyers. I mean it. There is interest aabout it, but not serious...
sorry for writing so much