First, you have not said this in so many words but it sounds like you expect people like my American citizen nanny to somehow obtain a different job that requires more skills (what you call specialize) and leave all the nanny jobs in this country to illegals. I guess you would have the same advice for her husband in the landscaping business. This is apparently what you call "division of labor." You seem willing to impose all the costs and inconveniences of employing illegals in this country on the people who are unfortunate enough to be in the position to have to compete with them. This is strangely reminiscent of an earlier era of "economic specialization" of the labor force in America during which slaves were imported to do the unskilled work -- which is perhaps why critics of illegal immigration frequently refer to it as "slave labor."
Of course, as soon as the illegals become legal, they will demand higher wages, vacation days, health care benefits and all the rest. The only reason illegal labor is cheaper is because it is illegal and because the business owners have been able to shift most of the true costs of their presence in this country (education, welfare, health care, prisons) to taxpayers. To use economic terms since you are seem to prefer them, they have internalized the benefits (profits) and externalized the costs. Employers of illegal aliens are receiving massive subsidies from the American taxpayer.
According to your reasoning, because of the presence of massive numbers of illegal workers in America we should all be living in the best of all possible times. This is self-evidently untrue. Living standards for the lower and middle classes in this country have declined and wages have not kept up with inflation. There is less, not more economic opportunity today for the unskilled worker or the worker who has only a high school education. In the 1950's and 60's, a time of very little immigration illegal or otherwise, my high school educated father was able to support a family of six in a comfortable middle class lifestyle on the wages he earned from delivering dry cleaning. Nothing like this opportunity is available today, nor would it have been for him if he had to compete with millions of illegal workers.
As to your question about consumer costs, I believe that in the end, we are all deluding ourselves in thinking that the cheap goods and labor costs afforded by illegal immigrants are a good bargain. I think most Americans understand this. We are subsidizing this insanity with our very lives (as the families of those who died on 9-11 can attest), with massive crime rates and prison costs, with skyrocketing welfare, defense and education costs, and most importantly with the destruction of the very economic and social conditions (an independent and self reliant population) that are required to maintain democratic self-government. If we added all these costs of illegal immigration to the prices of the goods and services they are involved in providing I doubt anyone would consider us better off in the bargain.
Oh, suddenly we care about this "scourge" and want to compare it to slavery to make the argument more dramatic? Maybe I'm imagining it but I thought illegal immigrants were coming in droves, voluntarily, so as to achieve something better. Now it's slavery? Oh my, you've certainly moved the bar on me now!
Julian Simon showed that immigrants -- even the illegal ones -- are more of a benefit to the economy, when all the costs and value are accounted for, then they are a drain on it. The data and research is about 20 years old though and things may have changed. If they did change, it is no doubt because of a change in entitlements -- entitlements that many unsavory-type American's are a larger consumer of (and at the good-standing American taxpayer's expense.)
Of course, as soon as the illegals become legal, they will demand higher wages, vacation days, health care benefits and all the rest. .
This is rich! Isn't this the very thing that you want for these people, especially with the "all the rest" comment? All the rest means to pay taxes and assimilate, right? Didn't you just become these slaves' champion earlier [And the bar moves a little further this time]?. A little consistency would be helpful here.