Yes Zoliborz and Wola are some of the better areas of Warsaw (you're right between the two). You're also just around the corner from the Arkadia shopping centre and close to the trams along Okopowa that are only a couple of minutes into the Centrum.
I would be careful about pricing though. House prices continue to rise a lot faster than wages in Poland so it's a high risk country. I think there could be major probles for so many investors trying to sell in a few years. Wages have either to catch up with housing, which is not likely with double digit growth, or prices have to come down to meet affordability. In the end you have to be able to sell it, so you're safer sticking to a market that you can sell to the locals, but if you want a punt in a high risk country then why not.