Stronger, yes. But ...

• It's far from clear that the central premise is correct. (Cambridge has a lot of immigrants and I think it's very nice. I'm told Stoke-on-Trent is pretty rubbish but it has few immigrants. Two cherry-picked cases don't tell you much about correlation but, hey, that's one more case than bramflakes offered.)
• The differential effects of immigration within a country might look different from the overall effects on the country as a whole. (Toy model, not intended to be a description of how things actually are: suppose some immigrant group produces disproportionate numbers of petty criminals and brilliant business executives; then maybe areas with more of that group will have more crime but by the magic of income tax the high earnings of the geniuses will make everyone better off.)
• For some people -- I am not claiming you are one -- the very fact that a place has more immigrants (or more of particular "types of immigrants", nudge nudge wink wink) makes it less nice. Those who happen not to feel that way may have a different view of the correlation between niceness and immigration from those who do. To take a special case, the immigrants themselves probably don't feel that way, and for some who favour liberal immigration policies the benefit to the immigrants is actually an important part of the point.