"我家有花" and "这里以前有桥" are legit sentences. By not having measure word and classifier, it mean "I have flower in my home" and "there used to be bridge here" -- The quantity or number is unspecified. It can be a single flower or a houseful of it; It can be a single bridge or a few of them. It just stated 'there's flower' and 'there's bridge' in general
If you add measure word and classifier, the quantity or number would become specific
我家有(兩盆)花 = I have (two pot of) flower in my home -- Not one, not three, but two
这里以前有(一座)桥 = "there used to be (a) bridge here" -- Not two, not three, but one
(1) 宿舍东便有商店，图书馆和食堂。 (2) 宿舍东边有一家商店，一家图书馆和一个食堂。
Both are correct.
Sentence (1) didn't state the number of the objects (there could be any number of stores, libraries and cafeterias)
Sentence (2) specifically stated the number of each object -- (one shop, one library and one cafeteria)