[Mythor]

To make the registration page not require the nospam question be answered if a user is already registered, you can alter the following line via the Manage Products section.
Edit the "register_addmember_process" script, the following line:

if ($vbulletin->options['nospam_onoff'] AND $vbulletin->options['nospam_use_reg'])

Change to:

if ($vbulletin->options['nospam_onoff'] AND $vbulletin->options['nospam_use_reg'] AND !$vbulletin->userinfo['userid'])

And registered members should no longer have to enter an answer to the NoSpam question (they won't see the box either).

Note: I make no promises as to how effective/safe/workable this alteration is, do it at your own risk, etc. It seems to be the way the Contact Us script is set up so it should be okay, but I am by no means an expert.

Hopefully antialiasis will come back with a better solution.