My problem with segulos and the like is that if you try to test them, somebody will label you an apikorus. For instance if there are 100 people looking for shidduchim, the way to test is to have 50 do segula X and the other 50 not. Then you compare success rates of each group.
It is interesting that the Rambam says we absolutely should test neviim by making them do a number of osos and mofsim before we believe their prophecy. Otherwise anybody can claim to be a navi. However, if you suggest this for segulos, people will quite rapidly get angry at you.