BM is a plus for Poor House -- but not as much of a plus as, say, Fishing Village and Spice Merchant and preferably some other good + buy as well
BM games tend to be so interesting that a lot more depends on what happens with it than on whether poor house is on the board with it
On a general note, BM tends to be disliked for its randoms/swingy nature -- which is a downside on its own, but those people tend to be under-appreciating the skill and tactical and strategic adaptations it takes to react to what comes out of the BM, both in your own deck and in your opponent's. It's a really fun card once you appreciate that angle