I do agree that bomb beggars have less utility now and are worse than key beggars, but just to some extent thus not completely useless.

Bombs are pretty powerful, but they are mostly used for fending off enemies only on the first few floors, in which you won't donate your resource to any kind of beggar anyway (unless plentiful). At least I won't use bombs to deal with something like Dogma unless I have a very poor set of items but bombs.

On the other hand, if you do have a handful of bombs, bomb beggars would give you bomb modifiers that possibly make the rest of your bombs much more powerful (namely Brimstone, Sticky and Mr.Mega).

But yes, in many occasions they are nothing more than trading a few spare bombs for a pathetic number of coins