Often migrants will repatriate some of their incomes back to their native homelands so yes Poland's economy would see the benefit from this when Poles who go abroad still have ties back home.
I wasn't thinking along those lines, more like it cut Polands potential unemployment rate.
I think there is some fact and some fiction in the rest you are saying. The town in which I live is mostly industrial/manufacturing. There has been a massive influx from Poland, Lithuania and Estonia with some from Portugal, former Yugoslavia and African countries. Seven years ago this was one of the whitest towns in England because the ******** that lived here before were racist beyond belief.
Contrary to the competition ideal, what actually happened here is this. The immigrants arrived and there were few jobs available. Their first port of call was the job agencies. The job agencies saw an angle on this. Instead of supplying school/college leavers they could supply adults for the same money. They knew the new arrivals were desperate an ill informed. They also knew the school leavers were using them as a step on the ladder upwards and were not long term prospects. From early 2005 I was getting weekly calls from agencies, blatantly transgressing UK employment laws, offering a new way of employing people including advice on how to get rid of existing staff. So we ended up with immigrants replacing school leavers and to be fair, these people were often put in difficult situations. 3 days work one week, a days work the next. Effectively keeping them in a desperate position. They had to work like trojans in a vain hope they were noticed. Nearly all of these were on minimum wage unless they had a special skill with certification that matched a UK standard. There cannot be many of these as I see no reason for them to leave Poland.
So what we have ended up with here is a lot of adults on minimum wage who have hours that are not guaranteed. Effectively a school leavers wage. Because there incomes are so low, what they pay in tax is returned in Working Tax Credits. School leavers that have had the bottom rung removed. I have to mention benefit fraud here too although it is a subject I usually avoid of PF. Some Poles figured out if they told the local council they were not partners and rented a 2 bedroom flat, they could sub let one room and one of them could claim an allowance towards their rent. £130 a month I think. This is a common benefit fraud. The smarter Poles figured out if they rented a 5 bedroomed house they could sub let and live for free. Good thinking! I agree the influx pushed rents up, but again, many landlords here are cash only. I doubt this is declared in full. For example the council rating here is £460/month for a three bedroomed house, whereas you would be hard pushed to find something under £600. Thats a £140 that the taxman doesn't need to know about. I'm sure they are more careful than that though. Schools have also had their budgets either stretched or enlarged because they have extra expenditure on teachers specifically for the ESL children. Lets say each ESL teacher is payed £18000 pa and we have 12 schools, thats a lot of cash to generate from tax. It doesn't add up.
I see a benefit regarding council tax. Its impossible to avoid realistically. Also the more people the local council have paying council tax, the more they get from central government. Council tax itself is another failure. Basing a tax on a property rather than occupation is dumb. Margaret Thatchers poll tax was the way forward, but the hideously inept implementation has ruled that out for the foreseeable future.
Overall in my particular location I think things have stood still or both the immigrants and the natives are losers. We just have more people speaking less English and the true effect will not be seen/revealed for another 10/20 years. If the immigrants had started businesses, and a minority have, then the situation would be significantly different.
This is how I see it where I live but it may be very different in other towns/cities.