Your post interested me because my great-great grandfather John Lewandowski was married to Mary Urban; they were both born in Poland and immigrated before 1900 to Albany, NY, as did Mary's parents, who were Valenti Urbaniak and Rose Stelmaszewska.I certainly cannot say that these families are related, but you never know without more digging.
As far as where you should look for more records - have you checked the cemetery's interment records?Neither John Lewandowski or Mary Urban Lewandowski have head stones, but the cemetery records at least provide a date when they were buried (and in some cases their parent's names and place of birth).
From the date of death/burial you can look for an obituary in the local paper (probably on microfilm at the library) and order their death certificates (either from the state - which takes forever - or through the clerk of the county in which they died).
Granted, the vital records fee has gone up absurdly high in NY State ($22!!), but it should at least tell you whether they were born in the US or Germany/Poland; and, if you are lucky might give you other important data (date of birth; parent's names, and idea of when they immigrated, etc.)
Look for a catholic church in their neighborhood which served the Polish community (in Buffalo I am sure there is one!); they might have death records for them, as well as other family records.
Of course there is always census data to search; they should be in the 1930 census... Check Frank, Frances, Steven and Stephen and don't be surprised if they are found as "Urbaniak" as my family in Albany seemed to go back and forth between Urbaniak and Urban.