yes, you're certainly right. I hate spam as well, and who doesn't?
We already have a question on the registration form in place in order to make automatic registrations by spam bots more difficult. Custom, unique questions are supposed to be one of the most effective measures against spam bots, and I can verify that they work well. (Have to change this one soon, though.) A problem with such questions is to come up with good ones: Ones that are in fact custom and mostly unique and can still be answered by humans.
On the other hand, I don't want to make the registration process for legitimate users overly hard or unnecessarily frustrating. I've been reluctant with e.g. the manual activation of user profiles by an admin, because that would force the user who registered for the forum (typically to ask a question or write a post) to wait hours or days until someone verified and activated his profile. As a compromise, I've chosen, along with the above question on the registration form, to check the forum regularly (typically once per day) and delete the occasional spam account manually (and tolerate the spam post until then).
Obviously, this is not ideal, but as forum spam seems to be declining anyway, it used to and seems to be a viable solution – with compromises.
I didn't know about the search by the "powered by" line in the footer though! It is certainly worth to consider taking it out, but note that the phpBB folk's rule was (and likely still is?) that they provide no support if this line is altered or removed. I've never needed such custom, board-specific support, but we would still remove their attribution line.
There is another consideration: I like this forum's style very well, but as Arty is no longer developing it, it is no longer compatible with the latest releases of phpBB, so we're stuck with a version of phpBB that is still good, but cannot easily be upgraded. Fortunately, it looks as if for a solution, we can soon take not one, but two steps forward: The phpBB dev team is planning a new style system and a new default theme, see https://blog.phpbb.com/2018/09/16/to-the-future/
for the plans. My intention is to wait until this is released, then upgrade phpBB and switch to the new default style (or a slight variant thereof). This will involve a customization step within which we can review issues with spam bot prevention.